Steam reactivation of spent CaO-based sorbent for multiple CO2 capture cycles

This study examines steam reactivation of sorbent to improve the reversibility of multiple CaO-CO2 capture cycles. Experiments to obtain spent sorbent were performed in a tube furnace, and reactivation was achieved using steam in a pressurized reactor. Sorbent activity for CO2 capture was then tested in a thermogravimetric analyzer (TGA), in multi-cycle carbonation tests. After reactivation the sorbent had even better characteristics for CO2 capture than that of the natural sorbent. The average carbonation degree over 10 cycles for the reactivated sorbent approached 70%, significantly higher than for the original sorbent (35-40%). This means that the same sorbent may achieve effective CO2 capture over a large number of cycles, in the absence of other phenomena such as attrition. Partially sulfated sorbents may also be reactivated, but hydration itself is also hindered by sulfation.     

Thermal activation of CaO-based sorbent and self-reactivation during CO2 capture looping cycles

In this study, the thermal activation of different types of CaO-based sorbents was examined. Pretreatments were performed at different temperatures (800--1300 degrees C) and different durations (6--48 h) using four Canadian limestones. Sieved fractions of the limestones, powders obtained by grinding, and hydroxides produced following multiple carbonation/calcination cycles achieved in a tube furnace were examined. Pretreated samples were evaluated using two types of thermogravimetric reactors/ analyzers. The most important result was that thermal pretreatment could improve sorbent performance. In comparison to the original, pretreated sorbents showed better conversions over a longer series of CO2 cycles. Moreover, in some cases, sorbent activity actually increased with cycle number, and this effectwas especially pronounced for powdered samples preheated at 1000 degrees C. In these experiments, the increase of conversion with cycle number (designated as self-reactivation) after 30 cycles produced samples that were approximately 50% carbonated for the four sorbents examined here, and there appeared to be the potential for additional increase. These results were explained with the newly proposed pore--skeleton model. This model suggests, in addition to changes in the porous structure of the sorbent, that changes in the pore--skeleton produced during pretreatment strongly influence subsequent carbonation/ calcination cycles.     

Effect of repeated steam hydration reactivation on CaO-based sorbents for CO2 capture

Samples of natural limestone and commercial calcium carbonate were subjected to successive calcination and carbonation reactions in a TGA and to repeated activity restoration by steam hydration. Steam hydration of spent lime, followed by heating in CO(2), was shown to be an effective method for repeatedly restoring high CO(2) capture activity to spent lime during a large number of CO(2) capture cycles. Steam hydration was also shown to reduce the decay rate of the CO(2) capture activity by increasing the rate of carbonation in the diffusion controlled regime. Repeated hydration-carbonation-calcination cycles led to a considerable expansion of the particles through the formation of large vesicles, likely to lead to high attrition levels when applied in fluidized beds. Based on SEM observation of the particles during hydration-carbonation-calcination cycling, a model was proposed for their progressive weakening. It was concluded that strategies to reduce this weakening must limit the growth of the cracks in the crystal as they are cycled repeatedly.     

Development of regenerable MgO-based sorbent promoted with K2CO3 for CO2 capture at low temperatures

To improve their CO2 absorption capacity, alkali-based sorbents prepared by impregnation and wet mixing method of potassium carbonate on supports such as activated carbon and MgO (KACI30, KACP30, KMgI30, and KMgP30), were investigated in a fixed bed reactor (C02 absorption at 50-100 degrees C and regeneration at 150-400 degrees C). Total CO2 capture capacities of KMgI30-500 and KMgP30-500 were 178.6 and 197.6 mg CO2/g sorbent, respectively, in the presence of 11 vol % H2O even at 50 degrees C. The large amount of CO2 capture capacity of KMgP30-500 and KMgI30-500 could be explained by the fact that MgO itself, as well as K2CO3, could absorb CO2 in the presence of water vapor even at low temperatures. In particular, water vapor plays an important role in the CO2 absorption of MgO and KMgI30-500 even at low temperatures below 60 degrees C, in marked contrast to MgO and CaO which can absorb CO2 at high temperatures. The CO2 capture capacity of the KMgI30-300 sorbent, however, was less than that of KMgI30-500 due to the formation of Mg(OH)2 which did not absorb CO2. MgO based-sorbents promoted with K2CO3 after CO2 absorption formed new structures such as K2Mg(CO3)2 and K2Mg(CO3)2 x 4(H2O), unlike KACI30 which showed only the KHCO3 crystal structure. The new Mg-based sorbents promoted with K2CO3 showed excellent characteristics in that it could satisfy a large amount of CO2 absorption at low temperatures, a high CO2 absorption rate, and fast and complete regeneration.     

Sequential capture of CO2 and SO2 in a pressurized TGA simulating FBC conditions

Four FBC-based processes were investigated as possible means of sequentially capturing SO2 and CO2. Sorbent performance is the key to their technical feasibility. Two sorbents (a limestone and a dolomite) were tested in a pressurized thermogravimetric analyzer (PTGA). The sorbent behaviors were explained based on complex interaction between carbonation, sulfation, and direct sulfation. The best option involved using limestone or dolomite as a SO2-sorbent in a FBC combustor following cyclic CO2 capture. Highly sintered limestone is a good sorbent for SO2 because of the generation of macropores during calcination/carbonation cycling.     

Moisture swing sorbent for carbon dioxide capture from ambient air

An amine-based anion exchange resin dispersed in a flat sheet of polypropylene was prepared in alkaline forms so that it would capture carbon dioxide from air. The resin, with quaternary ammonium cations attached to the polymer structure and hydroxide or carbonate groups as mobile counterions, absorbs carbon dioxide when dry and releases it when wet. In ambient air, the moist resin dries spontaneously and subsequently absorbs carbon dioxide. This constitutes a moisture induced cycle, which stands in contrast to thermal pressure swing based cycles. This paper aims to determine the isothermal performance of the sorbent during such a moisture swing. Equilibrium experiments show that the absorption and desorption process can be described well by a Langmuir isothermal model. The equilibrium partial pressure of carbon dioxide over the resin at a given loading state can be increased by 2 orders of magnitude by wetting the resin.     

Energy and material balance of CO2 capture from ambient air

Current Carbon Capture and Storage (CCS) technologies focus on large, stationary sources that produce approximately 50% of global CO2 emissions. We propose an industrial technology that captures CO2 directly from ambient air to target the remaining emissions. First, a wet scrubbing technique absorbs CO2 into a sodium hydroxide solution. The resultant carbonate is transferred from sodium ions to calcium ions via causticization. The captured CO2 is released from the calcium carbonate through thermal calcination in a modified kiln. The energy consumption is calculated as 350 kJ/mol of CO2 captured. It is dominated by the thermal energy demand of the kiln and the mechanical power required for air movement. The low concentration of CO2 in air requires a throughput of 3 million cubic meters of air per ton of CO2 removed, which could result in significant water losses. Electricity consumption in the process results in CO2 emissions and the use of coal power would significantly reduce to net amount captured. The thermodynamic efficiency of this process is low but comparable to other "end of pipe" capture technologies. As another carbon mitigation technology, air capture could allow for the continued use of liquid hydrocarbon fuels in the transportation sector.     

Cycle development and design for CO2 capture from flue gas by vacuum swing adsorption

CO2 capture and storage is an important component in the development of clean power generation processes. One CO2 capture technology is gas-phase adsorption, specifically pressure (or vacuum) swing adsorption. The complexity of these processes makes evaluation and assessment of new adsorbents difficult and time-consuming. In this study, we have developed a simple model specifically targeted at CO2 capture by pressure swing adsorption and validated our model by comparison with data from a fully instrumented pilot-scale pressure swing adsorption process. The model captures nonisothermal effects as well as nonlinear adsorption and nitrogen coadsorption. Using the model and our apparatus, we have designed and studied a large number of cycles for CO2 capture. We demonstrate that by careful management of adsorption fronts and assembly of cycles based on understanding of the roles of individual steps, we are able to quickly assess the effect of adsorbents and process parameters on capture performance and identify optimal operating regimes and cycles. We recommend this approach in contrast to exhaustive parametric studies which tend to depend on specifics of the chosen cycle and adsorbent. We show that appropriate combinations of process steps can yield excellent process performance and demonstrate how the pressure drop, and heat loss, etc. affect process performance through their effect on adsorption fronts and profiles. Finally, cyclic temperature profiles along the adsorption column can be readily used to infer concentration profiles-this has proved to be a very useful tool in cyclic function definition. Our research reveals excellent promise for the application of pressure/vacuum swing adsorption technology in the arena of CO2 capture from flue gases.     

CO2 capture in different carbon materials

In this work, the CO(2) capture capacity of different types of carbon nanofibers (platelet, fishbone, and ribbon) and amorphous carbon have been measured at 26 °C as at different pressures. The results showed that the more graphitic carbon materials adsorbed less CO(2) than more amorphous materials. Then, the aim was to improve the CO(2) adsorption capacity of the carbon materials by increasing the porosity during the chemical activation process. After chemical activation process, the amorphous carbon and platelet CNFs increased the CO(2) adsorption capacity 1.6 times, whereas fishbone and ribbon CNFs increased their CO(2) adsorption capacity 1.1 and 8.2 times, respectively. This increase of CO(2) adsorption capacity after chemical activation was due to an increase of BET surface area and pore volume in all carbon materials. Finally, the CO(2) adsorption isotherms showed that activated amorphous carbon exhibited the best CO(2) capture capacity with 72.0 wt % of CO(2) at 26 °C and 8 bar.     

Simultaneous removal of SO2 and trace SeO2 from flue gas: effect of SO2 on selenium capture and kinetics study

Sulfur dioxide (SO2) and trace elements are all pollutants derived from coal combustion. This study relates to the simultaneous removal of SO2 and trace selenium dioxide (SeO2) from flue gas by calcium oxide (CaO) adsorption in the moderate temperature range, especially the effect of SO2 presence on selenium capture. Experiments performed on a thermogravimetric analyzer (TGA) can reach the following conclusions. When the CaO conversion is relatively low and the reaction rate is controlled by chemical kinetics, the SO2 presence does not affect the selenium capture. When the CaO conversion is very high and the reaction rate is controlled by product layer diffusion, the SO2 presence and the product layer diffusion resistance jointly reduce the selenium capture. On the basis of the kinetics study, a method to estimate the trace selenium removal efficiency using kinetic parameters and the sulfur removal efficiency is developed.     

Novel regenerable sorbent for mercury capture from flue gases of coal-fired power plant

A natural chabazite-based silver nanocomposite (AgMC) was synthesized to capture mercury from flue gases of coal-fired power plants. Silver nanoparticles were engineered on zeolite through ion-exchange of sodium ions with silver ions, followed by thermal annealing. Mercury sorption test using AgMC was performed at various temperatures by exposing it to either pulse injection of mercury or continuous mercury flow. A complete capture of mercury by AgMC was achieved up to a capture temperature of 250 degrees C. Nano silver particles were shown to be the main active component for mercury capture by amalgamation mechanism. Compared with activated carbon-based sorbents, the sorbent prepared in this study showed a much higher mercury capture capacity and upper temperature limit for mercury capture. More importantly, the mercury captured by the spent AgMC could be easily released for safe disposal and the sorbent regenerated by simple heating at 400 degrees C. Mercury capture tests performed in real flue gas environment showed a much higher level of mercury capture by AgMC than by other potential mercury sorbents tested. In our mercury capture tests, the AgMC exposed to real flue gases showed an increased mercury capture efficiency than the fresh AgMC.     

A biomass-supported Na2CO3 sorbent for flue gas desulfurization

A novel sorbent for SO2 removal has been investigated. The sorbent is obtained by conventional incipient wetness impregnation of abandoned biomaterials (straw or dried leaves) with an aqueous solution of Na2CO3. A material with the composition 80 wt % Na2CO3/straw shows a desulfurization activity which is both higher and faster than that of the reference sample Na2CO3/gamma-Al2O3. The breakthrough and stoichiometric SO2 adsorption efficiencies for 80 wt % Na2CO3/straw reach 48.9% and 80.6%, respectively, at a temperature of 80 degrees C. The adsorption efficiencies are almost constant in the temperature range 70 to 300 degrees C. According to IR and XPS analysis the main products observed on the spent sorbent are sulfite below 150 degrees C and sulfate at 300 degrees C. The Na2CO3 in 80 wt % Na2CO3/straw can potentially be recycled by the oxidation of the straw with concomitant reduction of the sulfite species to elemental sulfur, making the proposed process CO2 neutral.     

Influence of the concentration of CO2 and SO2 on the absorption of CO2 by a lithium orthosilicate-based absorbent

A novel, high temperature solid absorbent based on lithium orthosilicate (Li(4)SiO(4)) has shown promise for postcombustion CO(2) capture. Previous studies utilizing a clean, synthetic flue gas have shown that the absorbent has a high CO(2) capacity, >25 wt %, along with high absorption rates, lower heat of absorption and lower regeneration temperature than other solids such as calcium oxide. The current effort was aimed at evaluating the Li(4)SiO(4) based absorbent in the presence of contaminants found in typical flue gas, specifically SO(2), by cyclic exposure to gas mixtures containing CO(2), H(2)O (up to 25 vol. %), and SO(2) (up to 0.95 vol. %). In the absence of SO(2), a stable CO(2) capacity of ～ 25 wt % over 25 cycles at 550 °C was achieved. The presence of SO(2), even at concentrations as low as 0.002 vol. %, resulted in an irreversible reaction with the absorbent and a decrease in CO(2) capacity. Analysis of SO(2)-exposed samples revealed that the absorbent reacted chemically and irreversibly with SO(2) at 550 °C forming Li(2)SO(4). Thus, industrial application would require desulfurization of flue gas prior to contacting the absorbent. Reactivity with SO(2) is not unique to the lithium orthosilicate material, so similar steps would be required for other absorbents that chemically react with SO(2).     

Application of amine-tethered solid sorbents for direct CO2 capture from the ambient air

While current carbon capture and sequestration (CCS) technologies for large point sources can help address the impact of CO(2) buildup on global climate change, these technologies can at best slow the rate of increase of the atmospheric CO(2) concentration. In contrast, the direct CO(2) capture from ambient air offers the potential to be a truly carbon negative technology. We propose here that amine-based solid adsorbents have significant promise as key components of a hypothetical air capture process. Specifically, the CO(2) capture characteristics of hyperbranched aminosilica (HAS) materials are evaluated here using CO(2) mixtures that simulate ambient atmospheric concentrations (400 ppm CO(2) = "air capture") as well as more traditional conditions simulating flue gas (10% CO(2)). The air capture experiments demonstrate that the adsorption capacity of HAS adsorbents are only marginally influenced even with a significant dilution of the CO(2) concentration by a factor of 250, while capturing CO(2) reversibly without significant degradation of performance in multicyclic operation. These results suggest that solid amine-based air capture processes have the potential to be an effective approach to extracting CO(2) from the ambient air.     

Enhancement of fast CO2 capture by a nano-SiO2/CaO composite at Ca-looping conditions

In this paper we show the performance of a new CO(2) sorbent consisting of a dry physical mixture of a Ca-based sorbent and a SiO(2) nanostructured powder. Thermo-gravimetric analysis (TGA) performed at conditions close to the Ca-looping process demonstrate that the rate of CO(2) capture by the mixture is enhanced during the fast carbonation stage of practical interest in applications. Moreover, the residual capture capacity of the mixture is increased. SEM/EDX, physisorption, and XRD analyses indicate that there is a relevant interaction between the nanostructured SiO(2) skeleton and CaO at high temperatures, which serves to improve the efficiency of the transfer of CO(2) to small reactive pores as well as the stability of the sorbent pore structure.     

Fluidized bed combustion systems integrating CO2 capture with CaO

Capturing CO2 from large-scale power generation combustion systems such as fluidized bed combustors (FBCs) may become important in a CO2-constrained world. Using previous experience in capturing pollutants such as SO2 in these systems, we discuss a range of options that incorporate capture of CO2 with CaO in FBC systems. Natural limestones emerge from this study as suitable high-temperature sorbents for these systems because of their low price and availability. This is despite their limited performance as regenerable sorbents. We have found a range of process options that allow the sorbent utilization to maintain a given level of CO2 separation efficiency, appropriate operating conditions, and sufficiently high power generation efficiencies. A set of reference case examples has been chosen to discuss the critical scientific and technical issues of sorbent performance and reactor design for these novel CO2 capture concepts.     

CO2 mitigation via capture and chemical conversion in seawater

A lab-scale seawater/mineral carbonate gas scrubber was found to remove up to 97% of CO(2) in a simulated flue gas stream at ambient temperature and pressure, with a large fraction of this carbon ultimately converted to dissolved calcium bicarbonate. After full equilibration with air, up to 85% of the captured carbon was retained in solution, that is, it did not degas or precipitate. Thus, above-ground CO(2) hydration and mineral carbonate scrubbing may provide a relatively simple point-source CO(2) capture and storage scheme at coastal locations. Such low-tech CO(2) mitigation could be especially relevant for retrofitting to existing power plants and for deployment in the developing world, the primary source of future CO(2) emissions. Addition of the resulting alkaline solution to the ocean may benefit marine ecosystems that are currently threatened by acidification, while also allowing the utilization of the vast potential of the sea to safely sequester anthropogenic carbon. This approach in essence hastens Nature's own very effective but slow CO(2) mitigation process; carbonate mineral weathering is a major consumer of excess atmospheric CO(2) and ocean acidity on geologic times scales.     

CO2 capture from the atmosphere and simultaneous concentration using zeolites and amine-grafted SBA-15

CO(2) capture from the atmosphere and concentration by cyclic adsorption-desorption processes are studied for the first time. New high microporosity materials, zeolite types Li-LSX and K-LSX, are compared to zeolite NaX and amine-grafted SBA-15 with low amine content. Breakthrough performance showed low silica type X (LSX) to have the most promise for application in dry conditions and capable of high space velocities of at least 63,000 h(-1), with minimal spreading of the CO(2) breakthrough curve. Amine-grafted silica was the only adsorbent able to operate in wet conditions, but at a lower space velocity of 1500 h(-1), due to slower uptake rates. The results illustrate that the uptake rate is as important as the equilibrium adsorbed amount in determining the cyclic process performance. Li-LSX was found to have double the capacity of zeolite NaX at atmospheric conditions, also higher than all other reported zeolites. It is further demonstrated that by using a combined temperature and vacuum swing cycle, the CO(2) concentration in the desorption product is >90% for all adsorbents in pellet form. This is the first report of such high CO(2) product concentrations from a single cycle, using atmospheric air.     

Cost structure of a postcombustion CO2 capture system using CaO

This paper presents the basic economics of an emerging concept for CO2 capture from flue gases in power plants. The complete system includes three key cost components: a full combustion power plant, a second power plant working as an oxy-fired fluidized bed calciner, and a fluidized bed carbonator interconnected with the calciner and capturing CO2 from the combustion power plant. The simplicity in the economic analysis is possible because the key cost data for the two major first components are well established in the open literature. It is shown that there is clear scope for a breakthrough in capture cost to around 15 $/t of CO2 avoided with this system. This is mainly because the capture system is generating additional power (from the additional coal fed to the calciner) and because the avoided CO2 comes from the capture of the CO2 generated by the coal fed to the calciner and the CO2 captured (as CaCO3) from the flue gases of the existing power plant, that is also released in the calciner.     

葡萄酒精中二氧化硫的去除

白兰地也称葡萄蒸馏酒，其生产工艺为：葡萄→检验→破碎→发酵→蒸馏→储存→勾兑→检验→冷冻→过滤→检验→封装→成品。严格的讲白兰地生产并不是简单的将葡萄原酒加以蒸馏而产生的，白兰地的生产工艺与葡萄酒生产工艺有着重要的区别：首先是原料上的区别，生产白兰地的葡萄要求成熟时含糖量低，酸度高，这样，单位白兰地原料酒中含有更丰富的芳香物质。然后是发酵工艺上的区别，在生产葡萄酒时SO2的添加是十分重要的，但白兰地生产中却严禁添加SO2，添加后将产生以下危害：①由于SO2的添加，使原料酒发酵变成了单纯的酒精发酵，损失…