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.     

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.     

SO2 retention by reactivated CaO-based sorbent from multiple CO2 capture cycles

This paper examines the reactivation of spent sorbent, produced from multiple CO2 capture cycles, for use in SO2 capture. CaO-based sorbent samples were obtained from Kelly Rock limestone using three particle size ranges, each containing different impurities levels. Using a thermogravimetric analyzer (TGA), the sulfation behavior of partially sulfated and unsulfated samples obtained after multiple calcination-carbonation cycles in a tube furnace (TF), following steam reactivation in a pressurized reactor, is examined. In addition, samples calcined/sintered under different conditions after hydration are also examined. The results show that suitably treated spent sorbent has better sulfation characteristics than that of the original sorbent. Thus for example, after 2 h sulfation, > 80% of the CaO was sulfated. In addition, the sorbent showed significant activity even after 4 h when > 95% CaO was sulfated. The results were confirmed by X-ray diffraction (XRD) analysis, which showed that, by the end of the sulfation process, samples contained CaSO4 with only traces of unreacted CaO. The superior behavior of spent reactivated sorbent appears to be due to swelling of the sorbent particles during steam hydration. This enables the development of a more suitable pore surface area and pore volume distribution for sulfation, and this has been confirmed by N2 adsorption-desorption isotherms and the Barrett-Joyner-Halenda (BJH) method. The surface area morphology of sorbent after reactivation was examined by scanning electron microscopy (SEM). Ca(OH)2 crystals were seen, which displayed their regular shape, and their elemental composition was confirmed by energy-dispersive X-ray (EDX) analysis. The improved characteristics of spent reactivated sorbent in comparison to the original and to the sorbent calcined under different conditions and hydrated indicate the beneficial effect of CO2 cycles on sorbent reactivation and subsequent sulfation. These results allow us to propose a new process for the use of CaO-based sorbent in fluidized bed combustion (FBC) systems, which incorporates CO2 capture, sorbent reactivation, and SO2 retention.     

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.     

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.     

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.     

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.     

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).     

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.     

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.     

三维网状形貌的SBA-15净化新材料

为了拦截卷烟主流烟气中的粒相物并去除烟草特有的亚硝胺TSNA,将具有三维网状结构的介孔材料SBA-15-fib尝试用于去除卷烟烟气中的粒相物和亚硝胺。实验表明,三维网状结构使得SBA-15材料能够有效地拦截卷烟烟气中的粒相物,减少焦油含量,同时将烟草特有亚硝胺TSNA在主流烟气中减少40%以上,其中NNN和NNK被去除得尤为明显。     

Optimisation of concentration of ingredients for simultaneous dyeing and finishing using response surface methodology

In the present study, simultaneous reactive dyeing and easy care finishing of cotton with a non-formaldehyde and environment-friendly compound (citric acid [CA]) was successfully optimised using a statistical model. An optimised recipe was formulated based on the half factorial central composite design and numerical optimisation solution by Design-Expert 6.0 software. The optimised conditions were investigated for the concentration of CA, catalyst, reactive dye, alkali and urea. Evaluation of the recipe was made with respect to K/S, percent fixation of reactive dye, dry crease recovery angle and tensile strength. The simultaneous dyeing and finishing using theoretical optimised recipe was carried out and performance of the sample was compared with the sample using conventional two-step dyeing and finishing process.     

Effects of bonding types and functional groups on CO2 capture using novel multiphase systems of liquid-like nanoparticle organic hybrid materials

Novel liquid-like nanoparticle organic hybrid materials (NOHMs) which possess unique features including negligible vapor pressure and a high degree of tunability were synthesized and their physical and chemical properties as well as CO(2) capture capacities were investigated. NOHMs can be classified based on the synthesis methods involving different bonding types, the existence of linkers, and the addition of task-specific functional groups including amines for CO(2) capture. As a canopy of polymeric chains was grafted onto the nanoparticle cores, the thermal stability of the resulting NOHMs was improved. In order to isolate the entropy effect during CO(2) capture, NOHMs were first prepared using polymers that do not contain functional groups with strong chemical affinity toward CO(2). However, it was found that even ether groups on the polymeric canopy contributed to CO(2) capture in NOHMs via Lewis acid-base interactions, although this effect was insignificant compared to the effect of task-specific functional groups such as amine. In all cases, a higher partial pressure of CO(2) was more favorable for CO(2) capture, while a higher temperature caused an adverse effect. Multicyclic CO(2) capture tests confirmed superior recyclability of NOHMs and NOHMs also showed a higher selectivity toward CO(2) over N(2)O, O(2) and N(2).     

超临界CO_2在填料塔中连续浓缩鱼油EPA和DHA工艺研究

突破鱼油有效组分间歇萃取的方法 ,设计建造了超临界CO2 在14mm填料塔中连续萃取浓缩鱼油有效组分的流程。通过试验 ,初步得到了工艺参数的范围 :分离柱压为 8～ 17MPa ,以 13MPa为宜 ;CO2 流量为 2～ 15L/min ;鱼油进料流量以 0 5～2mL/min为宜 ;柱的温度分布对分离效果有较大影响 ,3 6～ 85℃的范围是适宜的。控制柱底端和顶部的温度可以有效控制柱两端物料的流出量 ,从而控制有效物的回收率。     

Supercritical CO2 oil extraction from Chinese star anise seed and simultaneous compositional analysis using HPLC by fluorescence detection and online atmospheric CI‐MS identification

BACKGROUND: Supercritical CO₂ was utilised to extract Chinese star anise seed oil (CSASO), and a three‐level Box–Behnken factorial design from response surface methodology was applied to optimise the extraction conditions, including pressure, temperature and amount of modifier (ethanol). The compositional analysis of fatty acids in CSASO was performed by HPLC with fluorescence detection using 2‐(11H‐benzo[a]carbazol‐11‐yl)‐ethyl‐4‐methylbenzenesulfonate (BCETS) as labelling reagent. Identification was carried out by online atmospheric chemical ionisation–mass spectrometry. RESULTS: The optimum extraction conditions were as follows: extraction pressure, 27.72 MPa, extraction temperature, 46.22 °C, and amount of modifier, 8.58 vol.%. The experimental result showed that the maximum extraction yield was 25.31 ± 0.22% (w/w) under the conditions proposed. The compositional analysis indicated that CSASO mainly contained C18:2, C18:1, C18:3, C20:4, C16, C18 and C20 fatty acids. CONCLUSION: In this study, a fast, simple and high‐efficiency supercritical technique for extracting oil from Chinese star anise seed was developed. Simultaneous determination of fatty acids in CSASO using BCETS as the labelling reagent with HPLC fluorescence detection and online mass spectroscopy identification has been successfully achieved. Copyright © 2010 Society of Chemical Industry     

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.     

Characterization of the enhancement effect of Na2CO3 on the sulfur capture capacity of limestones

It has been known for a long time that certain additives (e.g., NaCl, CaCl2, Na2CO3, Fe2O3) can increase the sulfur dioxide capture-capacity of limestones. In a recent study we demonstrated that very small amounts of Na2CO3 can be very beneficial for producing sorbents of very high sorption capacities. This paper explores what contributes to these significant increases. Mercury porosimetry measurements of calcined limestone samples reveal a change in the pore-size from 0.04-0.2 microm in untreated samples to 2-10 microm in samples treated with Na2CO3--a pore-size more favorable for penetration of sulfur into the particles. The change in pore-size facilitates reaction with lime grains throughout the whole particle without rapid plugging of pores, avoiding premature change from a fast chemical reaction to a slow solid-state diffusion controlled process, as seen for untreated samples. Calcination in a thermogravimetric reactor showed that Na2CO3 increased the rate of calcination of CaCO3 to CaO, an effect which was slightly larger at 825 degrees C than at 900 degrees C. Peak broadening analysis of powder X-ray diffraction data of the raw, calcined, and sulfated samples revealed an unaffected calcite size (approximately 125-170 nm) but a significant increase in the crystallite size for lime (approximately 60-90 nm to approximately 250-300 nm) and less for anhydrite (approximately 125-150 nm to approximately 225-250 nm). The increase in the crystallite and pore-size of the treated limestones is attributed to an increase in ionic mobility in the crystal lattice due to formation of vacancies in the crystals when Ca is partly replaced by Na.     

Characterizing geochemical reactions in unsaturated mine waste-rock piles using gaseous O2, CO2, 12CO2, and 13CO2

In situ determinations of geochemical reaction rates in mine waste-rock piles remain a challenge. Depth-profiles of field O2 and CO2 pore-gas concentrations, delta13C(CO2) values, and moisture contents were used to characterize and quantify geochemical reaction rates in two waste-rock piles at the Key Lake Uranium Mine in northern Saskatchewan, Canada. Traditionally, the presence of O2 concentrations less than atmospheric in waste-rock piles has been attributed to mineral oxidation. This study showed that the interpretation of O2 and CO2 concentration profiles alone could not be used to identify the depths of dominant geochemical reactions in the piles and could lead to erroneous estimates of reaction rates. Modeling of the delta13C(CO2) depth profiles clearly showed that the gas concentration profiles present in the piles were the result of the oxidation of organic matter present below the piles, a mechanism not previously reported in the literature. Based on these findings, the rates of reactions in the organic zone were determined. The oxidation of organic matter at the base of waste-rock piles should be considered in future mine-waste pore-gas studies, in addition to sulfide oxidation and carbonate buffering.     

Study the kinetics and thermodynamics conditions for CO2 hydrate formation in orange juice concentration

In this study, for concentration of orange juice, two laboratory systems were used; one for CO₂ hydrate formation at high-pressure system, another for formation of THF hydrate at atmospheric pressure system. In the high-pressure system, the kinetic parameters of CO₂ hydrate formation in orange juice were investigated in comparison with pure water, in constant temperature and volume. Also the effect of the initial pressure (20, 30 and 35 bar), temperature (2, 3 and 4 °C) and brix (10, 13 and 16) were investigated on hydrate formation conditions. The results showed that, with increasing the pressure and lowering temperature, the initial rate of formation CO₂ hydrate is increased and the relaxation time is decreased. With increasing the brix, the initial rate of CO₂ hydrate formation is decreased and the relaxation time is increased. The maximum relaxation time of 1230 s was reached at 20 bar, 4 °C and 16 brix. It was determined that the content of orange juice plays as an inhibitor in hydrate formation. In the atmospheric system, the effect of brix (7, 10, 13, 16 and 20) on kinetics of THF hydrate formation was investigated in orange juice. After the separation of the formed crystals, the secondary brix was measured; the highest concentration in the initial brix of 7 was obtained about 200%., with increasing the brix, the induction time was increased, while it had no effect on the relaxation time.     

CO2气调解除后大米蒸煮特性、质构特性及食味品质的变化研究

为研究CO2气调储藏解除后大米蒸煮特性、质构特性及食味品质的变化规律,模拟我国典型储粮区的环境条件（35℃、80%RH和30℃、70%RH）,并以室温储藏（平均温度约20℃）为对照,进行储藏试验。结果表明：解除CO2气调后,大米在各模拟储藏条件下其米汤干物质、米汤pH值、米汤碘蓝值、弹性、黏着性、凝聚性均随储藏时间延长逐渐减小,吸水率、硬度、胶黏性、咀嚼性呈逐渐增加的趋势。室温储藏的大米,其米饭食味评分值下降相对35℃、80%RH和30℃、70%RH条件下的大米较缓慢,35℃、80%RH条件下储藏的大米在75 d后时检出霉菌。大米在室温和30℃、70%RH条件下储藏150和125 d后感官评分降至70分以下。大米在室温,30℃、70%RH和35℃、80%RH最佳食味品质保质期分别为150、125和75 d。