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1.
With the aim to enhance the CO2 capture capacity and anti‐attrition property of CaO‐based sorbents simultaneously, a novel CaO‐based sphere was prepared by extrusion‐spheronization using Ca(OH)2 powder with glucose templating. The CO2 capture characteristics and attrition resistance property of the sorbent were examined and the microstructure of the sorbents was analyzed. The results demonstrate that the obtained spherical sorbents exhibit an outstanding anti‐attrition performance compared to limestone sorbent. After 100 cycles, all of the templated sorbents hold a CO2 capture capacity of more than one time higher than that of limestone. The optimum templating rate of glucose in the sorbent was 1–5 wt %.  相似文献   

2.
This study focuses on enhancing CO2 uptake by modifying limestone with acetate solutions under pressurized carbonation condition. The multicycle tests were carried out in an atmospheric calcination/pressurized carbonation reactor system at different temperatures and pressures. The pore structure characteristics (BET and BJH) were measured as a supplement to the reaction studies. Compared with the raw limestone, the modified sorbent showed a great improvement in CO2 uptake at the same reaction condition. The highest CO2 uptake was obtained at 700 °C and 0.5 MPa, by 88.5% increase over the limestone at 0.1 MPa after 10 cycles. The structure characteristics of the sorbents on N2 absorption and SEM confirm that compared with the modified sorbent, the effective pores of limestone are greatly driven off by sintering, which hinders the easy access of CO2 molecules to the unreacted-active sites of CaO. The morphological and structural properties of the modified sorbent did not reveal significant differences after multiple cycles. This would explain its superior performance of CO2 uptake under pressurized carbonation. Even after 10 cycles, the modified sorbent still achieved a CO2 uptake of 0.88.  相似文献   

3.
Mechanical degradation of the solid particles used in sorption-enhanced steam methane reforming (SE-SMR) was investigated in a gas jet attrition apparatus. The performance of a dolomite, a limestone and a commercial reforming catalyst were compared based on the air jet attrition index (AJI). The dolomite showed the poorest resistance to attrition, likely due to the extra pore volume caused by calcination of MgCO3. The degree of loss of fines from the catalyst was significant, pointing to the need to develop catalysts suited to fluidized bed operation. Co-fluidization of the harder catalyst and the dolomite did not lead to additional attrition of the dolomite.  相似文献   

4.
Steel slag was used as a low‐cost feedstock to prepare CaO‐based sorbents for CO2 capture by acidification treatment, and the acidification process was optimized. Four main acidification parameters (i.e., extraction time, extraction temperature, acetic acid concentration, and solid/liquid ratio) were investigated. The solid/liquid ratio and extraction time are the most important factors that affect the CO2 capture capacity and stability of the sorbents. The CO2 sorption performance of optimal steel‐slag‐derived sorbent is more stable than that of naturally occurring limestone, due to the low Si/Ca ratio and the presence of MgO with high anti‐sintering ability. CaO‐based pellets with high resistance to attrition and compression were produced by extrusion of the steel‐slag‐derived sorbent powders.  相似文献   

5.
The calcination/carbonation loop of calcium-based (Ca-based) sorbents is considered as a viable technique for CO2 capture from combustion gases. Recent attempts to improve the CO2 uptake of Ca-based sorbents by adding calcium lignosulfonate (CLS) with hydration have succeeded in enhancing its effectiveness. The optimum mass ratio of CLS/CaO is 0.5 wt.%. The reduction in particle size and grain size of CaO appeared to be parts of the reasons for increase in CO2 capture. The primary cause of increase in reactivity of the modified sorbents was the ability of the CLS to retard the sintering rate and thus to remain surface area and pore volume for reaction. The CO2 uptake of the modified sorbents was also enhanced by elevating the carbonation pressure. Experimental results indicate that the optimal reaction condition of the modified sorbents is at 0.5 MPa and 700 °C and a high conversion of 0.7 is achieved after 10 cycles, by 30% higher than that of original limestone, at the same condition.  相似文献   

6.
The cyclic carbonation performances of shells as CO2 sorbents were investigated during multiple calcination/carbonation cycles. The carbonation kinetics of the shell and limestone are similar since they both exhibit a fast kinetically controlled reaction regime and a diffusion controlled reaction regime, but their carbonation rates differ between these two regions. Shell achieves the maximum carbonation conversion for carbonation at 680–700 °C. The mactra veneriformis shell and mussel shell exhibit higher carbonation conversions than limestone after several cycles at the same reaction conditions. The carbonation conversion of scallop shell is slightly higher than that of limestone after a series of cycles. The calcined shell appears more porous than calcined limestone, and possesses more pores > 230 nm, which allow large CO2 diffusion‐carbonation reaction rates and higher conversion due to the increased surface area of the shell. The pores of the shell that are greater than 230 nm do not sinter significantly. The shell has more sodium ions than limestone, which probably leads to an improvement in the cyclic carbonation performance during the multiple calcination/carbonation cycles.  相似文献   

7.
Calcium-based carbon dioxide sorbents were made in the gas phase by scalable flame spray pyrolysis (FSP) and compared to the ones made by calcination (CAL) of selected calcium precursors. Such flame-made sorbents consisted of nanostructured CaO and CaCO3 with twice as much specific surface area (40-60 m2/g) as the CAL-made sorbents. All FSP-made sorbents exhibited faster and higher CO2 uptake capacity than all CAL-made sorbents at intermediate temperatures. CAL of calcium acetate monohydrate resulted in sorbents with the best CO2 uptake among all CAL-made ones. At higher temperatures both FSP- and CAL-made sorbents (esp. from CaAc2·H2O) exhibited very high initial molar conversions (95%) but sintering contributed to grain growth that reduced the molar conversion down to 50%. In multiple carbonation/decarbonation cycles, the nanostructured FSP-made sorbents demonstrated stable, reversible and high CO2 uptake capacity sustaining maximum molar conversion at about 50% even after 60 such cycles, indicating high potential for CO2 uptake. The top performance of flame-made sorbents is best attributed to their nanostructure (30-50 nm grain size) that allows operation in the reaction-controlled carbonation regime rather than in the diffusion-controlled one when sorbents made with larger particles are employed.  相似文献   

8.
The activation of carbon sorbents in CO2 is investigated. The sorbents are produced by the thermolysis of naturally oxidized SS coal steeped in potassium hydroxide, with an alkali/coal ratio R KOH = 0.01 and 0.05 g/g. The influence of CO2 activation on the texture of the sorbents obtained is established. After 10-min activation, the increase in specific surface area of the sorbents is a maximum (about 100%). Longer activation increases the loss of material. The pore volume formed on activation is proportional to the proportion of carbon-bearing material removed. The volume of adsorbing pores formed in the sorbents is greatest when the loss of material is 25–35%.  相似文献   

9.
A synthetic, Ca-based solid sorbent, showed a marked increase in its ultimate uptake for CO2 at temperatures in excess of 750 °C when the concentration of CO2 was increased during carbonation in a fluidised bed. In contrast, the uptakes by natural sorbents, e.g. dolomite, were relatively insensitive to the concentration of CO2. It is apparent that the rate of reaction of the synthetic sorbent falls to zero once the small pores within the grains, of which the particle is composed, have largely filled and a thin layer of product has been deposited around each grain. To quantify this effect, theory has been developed in which the mechanical work required to disrupt the layer of product is taken into account. The resulting model for the overall uptake correlates experimental measurements well, except in circumstances where carbonation times are so long that sintering introduces gross changes in the morphology of the layer of product. The explanation for why the overall conversion of the synthetic sorbent is dependent on the concentration of CO2, whilst the conversion of dolomite is insensitive to [CO2], is attributed to differences in the yield stress, σY, needed to disrupt the layer of product formed in the two materials. It was found that the value of σY for dolomite is about an order of magnitude larger than that for the synthetic sorbent. The behaviour of the synthetic sorbent in response to increasing concentrations of CO2 makes it an attractive solid for the separation of CO2 from, e.g. the flue gases arising from combustion. By subsequently calcining the resulting solid, a pure stream of CO2 can be produced whilst the sorbent is regenerated for further use.  相似文献   

10.
Layered double hydroxide (LDH), one of representative high-temperature CO2 sorbents, has many advantages, including stable CO2 sorption, fast sorption kinetics, and low regeneration temperature. However, CO2 sorption uptake on LDH is not high enough for practical use; thus it is usually enhanced by impregnation with alkali metals such as K2CO3. In this study, LDH was impregnated with Na2CO3, and analyses based on scanning electron microscopy, N2 gas physisorption, in situ X-ray diffraction, and Fourier transform infrared spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of CO2 sorption. Although the surface area of LDH decreased after Na2CO3 impregnation, CO2 sorption uptake was greatly enhanced by the additional basicity of Na2CO3. The crystal structure of Na2CO3 in the Na2CO3-impregnated LDH changed from monoclinic to hexagonal with increasing temperature, and the sorbed-CO2 was stored in the form of carbonate. Thermogravimetric analysis was used to measure CO2 sorption uptake at 200–600 °C. The sample of Na2CO3: LDH=0.35: 1 weight ratio had the largest CO2 sorption uptake among the tested sorbents, and the CO2 sorption uptake tended to increase even after 400 °C.  相似文献   

11.
The calcium‐based sorbent cyclic calcination/carbonation reaction is an effective technique for capturing CO2 from combustion processes. The CO2 capture capacity for CaO modified with ethanol/water solution was investigated over long‐term calcination/carbonation cycles. In addition, the SEM micrographs and pore structure for the calcined sorbents were analyzed. The carbonation conversion for CaO modified with ethanol/water solution is greater than that for CaO hydrated with distilled water and is much higher than that for calcined limestone. Modified CaO achieves the highest conversion for carbonation at the range of 650–700 °C. Higher values of ethanol concentration in solution result in higher carbonation conversion for modified CaO, and lead to better anti‐sintering performance. After calcination, the specific surface area and pore volume for modified CaO are higher than those for hydrated CaO, and are much greater than those for calcined limestone. The ethanol molecule enhances H2O molecule affinity and penetrability to CaO in the hydration reaction so that the pores in CaO modified are obviously expanded after calcination. CaO modified with ethanol/water solution can act as a new and promising type of calcium‐based regenerable CO2 sorbent for industrial applications.  相似文献   

12.
采用不同体积浓度的乙醇溶液分别对石灰石和石灰石的煅烧产物CaO进行调质处理,研究它们的碳酸化反应,并与水合调质CaO的碳酸化进行比较。通过SEM和N2吸附法考察吸收剂多次煅烧的微观结构特性,进一步揭示了乙醇溶液促进CaO碳酸化的机理。结果表明:随着循环反应次数的增加,乙醇溶液调质后CaO的碳酸化转化率明显高于石灰石和水合调质的CaO,对于石灰石,乙醇溶液则没有明显的调质效果。CaO经乙醇溶液调质后在650~700℃内有利于碳酸化的进行。乙醇浓度越高,则经调质后CaO的转化率越高,抗烧结性能越好。经乙醇溶液调质的CaO煅烧后比表面积和比孔容均比单纯水合大,远高于煅烧后的石灰石;比孔容分布和孔比表面积分布明显优于煅烧后的水合CaO和石灰石。乙醇溶液调质对CaO的孔有明显的增扩效应。  相似文献   

13.
The dynamic adsorption behavior of CO2 under both nonisothermal and nearly isothermal conditions in silica supported poly(ethylenimine) (PEI) hollow fiber sorbents (Torlon®‐S‐PEI) is investigated in a rapid temperature swing adsorption (RTSA) process. A maximum CO2 breakthrough capacity of 1.33 mmol/g‐fiber (2.66 mmol/g‐silica) is observed when the fibers are actively cooled by flowing cooling water in the fiber bores. Under dry CO2 adsorption conditions, heat released from the CO2‐amine interaction increases the CO2 breakthrough capacity by reducing the severity of the diffusion resistance in the supported PEI. This internal resistance can also be alleviated by prehydrating the fiber sorbent with a humid N2 feed. The CO2 breakthrough capacity of prehydrated fibers is adversely affected by the release of the adsorption enthalpy (unlike the dry fibers); however, active cooling of the fiber results in a constant CO2 breakthrough capacity even at high CO2 delivery rates (i.e., high adsorption enthalpy delivery rates). In full RTSA cycles, a purity of 50% CO2 is achieved and the adsorption enthalpy recovery rate can reach ~72%. Studies on the cyclic stability of uncooled fiber sorbents in the presence of SO2 and NO contaminants indicate that exposure to NO at 200 ppm over 120 cycles does not lead to a significant degradation of the sorbents, but SO2 exposure at a similar high concentration of 200 ppm causes 60% loss in CO2 breakthrough capacity after 120 cycles. A simple amine reinfusion technique is successfully demonstrated to recover the adsorption capacity in poisoned fiber sorbents after deactivation by exposure to impurities such SO2. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3878–3887, 2014  相似文献   

14.
Calcium looping process is a promising approach for CO2 capture from the flue gas of fossil fuel power plants and the cement industry. Even though the advantages of calcium-based sorbents are low cost and high uptake capacity, they suffer from low durability during cycles. Modified sorbents were fabricated by adding alumina and zirconia and the mixture of alumina and zirconia to calcium oxide via the co-precipitation method. The performance of synthesized sorbents in terms of stability and CO2 capture capacity were evaluated using a fixed bed reactor in various CO2 sorption/desorption cycles. The sorbents were fabricated by a co-precipitation methodology using 10% binders (alumina and/or silica). X-ray diffraction (XRD), BET/BJH, and scanning electron microscopy (SEM) were conducted for characterization of synthesized sorbents. CaO-10% ZrO2 showed the best performance among the fabricated sorbents in terms of stability during 5 cycles and CO2 capacity (14 mmol CO2/g sorbent). The formation of CaZrO3 with a perovskite structure and high-temperature resistance could be attributed to well performance of zirconia-supported sorbent. On the other hand, no sign of aluminum zirconate formation was approved in XRD analysis for the fabricated sorbent using mixed binders of zirconia and alumina to enhance its stability during cycles.  相似文献   

15.
A possibility to carry out sorption-enhanced gasification (SEG) is represented by its integration with the calcium looping concept in dual interconnected fluidized beds (DIFB). This article is focused on the sorbent CO2 uptake performance and attrition/fragmentation tendency when operating conditions simulating those of a DIFB-SEG process are adopted. Experiments were carried out on a commercial Italian limestone in a laboratory-scale DIFB reactor. Carbonation was carried out in a range of test conditions, including variable temperature (600–700°C) and absence/presence of steam (10% by volume); CO2 concentration was set at 10% by volume. The characterization is extended by investigating the behavior of preprocessed DIFB-SEG samples on impact fragmentation tests, conducted in an ex situ apparatus. Tests were carried out for impact velocities in the range 17–45 m/s. Results were discussed considering both the impact velocity value and the operating conditions under which the sample was preprocessed in the fluidized bed.  相似文献   

16.
In this paper, an experimental study on the primary fragmentation and attrition of 5 limestones in a fluidized bed was conducted. The intensity of fragmentation and attrition were measured in the same apparatus but at different fluidizing velocities. It was found that the averaged size of the particles decreased by about 10-20% during the fragmentation process. The important factors for particle comminution include limestone types, heating rate, calcination condition and ambient CO2 concentration. Fragmentation mainly occurred in the first a few minutes in the fluidized bed and it was more intense than that in the muffle furnace at the same temperature. The original size effect was ambiguous, depending on the limestone type. The comminution caused by attrition mainly occurred during calcination process rather than sulphation process. The sulphation process was fragmentation and attrition resisted. The attrition rate of sulphate was similar to that of lime in trend, decaying exponentially with time, but was one-magnitude-order smaller than that of lime. Present experimental results indicate that fragmentation mechanism of the limestone is dominated by CO2 release instead of thermal stress.  相似文献   

17.
Integrated CO2 capture and conversion (ICCC) is a promising technology aiming at converting waste CO2 to fuels and high value-added chemicals. Herein, we described a proof-of-concept study of applying engineered natural ores (dolomite, magnesite, and limestone) to two different ICCC processes—intermediate-temperature ICCC for CH4 production (350–400°C) and high-temperature ICCC for syngas production (650–700°C). In the former process, a MgO-based CO2 sorbent prepared from dolomite and magnesite was combined with a methanation catalyst in a dual-bed configuration, whereby a CH4 yield of 7.1–7.3 mmol/g can be stably achieved per cycle over 20 consecutive ICCC cycles. In the latter process, a CaO-based sorbent derived from dolomite and limestone was coupled with a reforming catalyst also in a dual-bed mode, whereby syngas with a H2/CO ratio of 0.9–1.0 can be produced over 20 cycles. This study will expand the application of natural ores in CO2 emission reduction.  相似文献   

18.
CO2 capture systems based on the carbonation/calcination loop have gained rapid interest due to promising carbonator CO2 capture efficiency, low sorbent cost and no flue gases treatment is required before entering the system. These features together result in a competitively low cost CO2 capture system. Among the key variables that influence the performance of these systems and their integration with power plants, the carbonation conversion of the sorbent and the heat requirement at calciner are the most relevant. Both variables are mainly influenced by CaO/CO2 ratio and make-up flow of solids. New sorbents are under development to reduce the decay of their carbonation conversion with cycles. The aim of this study is to assess the competitiveness of new limestones with enhanced sorption behaviour applied to carbonation/calcination cycle integrated with a power plant, compared to raw limestone. The existence of an upper limit for the maximum average capture capacity of CaO has been considered. Above this limit, improving sorbent capture capacity does not lead to the corresponding increase in capture efficiency and, thus, reduction of CO2 avoided cost is not observed. Simulations calculate the maximum price for enhanced sorbents to achieve a reduction in CO2 removal cost under different process conditions (solid circulation and make-up flow). The present study may be used as an assessment tool of new sorbents to understand what prices would be competitive compare with raw limestone in the CO2 looping capture systems.  相似文献   

19.
Armin Hassanzadeh 《Fuel》2010,89(6):1287-1297
Highly reactive and mechanically strong low-cost regenerable MgO-based sorbents were prepared by modification of dolomite which involved partial calcinations followed by impregnation with a potassium-based salt. The sorbents are capable of removing CO2 from gasification-based processes such as Integrated Gasification Combined Cycle (IGCC). The sorbents have high reactivity and good capacity toward CO2 absorption in the temperature range of 300-450 °C at 20 atm. and can be easily regenerated at 500 °C. The reaction appears to be first order with respect to CO2 concentration with an activation energy of 44 kJ/mol. The reactivity and the absorption capacity of the sorbents increase with increasing temperature, as long as the partial pressure of CO2 is above the equilibrium value for sorbent carbonation. The reactivity of the sorbents appears to improve in the presence of steam, which is likely due to the increase in the BET surface area and the porosity of the sorbent. A two-zone expanding grain model, consisting of a high-reactivity outer shell and a low-reactivity inner core is shown to provide an excellent fit to the TGA experimental data on sorbent carbonation at various operating conditions.  相似文献   

20.
In both pressurized and oxygen-enriched fluidized bed combustion the partial pressure of CO2 in the reactor becomes high, which affects SO2 capture by limestone. Both of these technologies are also applicable to decreasing greenhouse gas emissions; the first one by increasing the efficiency of electric energy production and the latter by enabling capture of carbon dioxide for storage.Attrition increases the reaction rate by removing the sulphated layer on the particle, thus reducing the diffusion resistance. In the well-known solution for the shrinking core model the reaction time can be presented as the sum of the contributions of the kinetics and diffusion. It is shown that the effect of attrition can be expressed as an auxiliary term in this expression. A method to extract the diffusivity of the product layer from the SO2 response in a bench-scale fluidized bed test using a limestone sample with a wide particle size distribution is presented. Based on a population balance model, a method to estimate the particle-size-dependent attrition rate from measured particle size distributions of the feed and bed material is illustrated for a 71-MWe pressurized power plant. In addition attrition and its effect on the optimization of the limestone particle size for sulphur capture in oxygen-enriched combustion are discussed.  相似文献   

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