The Ca-based sorbent looping cycle represents an innovative way of CO 2 capture for power plants. However, the CO 2 capture capacity of the Ca-based sorbent decays sharply with calcination/carbonation cycle number increasing. In order to improve the CO 2 capture capacity of the sorbent in the Ca looping cycle, limestone was modified with acetic acid solution. The cyclic carbonation behaviors of the modified and original limestones were investigated in a twin fixed-bed reactor system. The modified limestone possesses better cyclic carbonation kinetics than the original limestone at each cycle. The modified limestone carbonated at 640-660°C achieves the optimum carbonation conversion. The acetic acid modification improves the long-term performance of limestone, resulting in directly measured conversion as high as 0.4 after 100 cycles, while the original limestone remains at a conversion of less than 0.1 at the same reaction conditions. Both the pore volume and pore area distributions of the calcines derived from the modified limestone are better than those derived from the original limestone. The CO 2 partial pressure for carbonation has greater effect on conversion of the original limestone than on that of the modified sorbent because of the difference in their pore structure characteristics. The carbonation conversion of the original limestone decreases with the increase in particle size, while the change in particle size of the modified sorbent has no clear effect on cyclic carbonation behavior.
In this paper, a reactor-like spinneret is proposed to generate a continuous hollow hydrogel fiber. In order to reliably control the deforming dynamics, the components of the spinneret are standardized in order to ease the online observation of morphological evolution. We found that not only did a co-flow occur in the tubular space, but a relatively large shrinkage of the shell layer at the outlet also occurred. Whereupon a weak coupling of the velocity field and diffusion-reacting co-flow was developed to describe the monitored co-flow morphology and to simulate the intermediate state of the concentration field, as well as to calculate the shrinkage profile with an integral formula. And a critical isogram [G]cri was determined to correspond to the morphological segmental feature, to trigger gelation and shrinkage as a threshold of solubility and the integral upper limit of the shrinkage region. Experimental evidence indicates that: the simulation is able to effectively predict the inner diameter of the hollow fiber; the transient inner diameter of the fiber at the outlet is expanded by approximately 70 μm (co-flow distance = 15 mm) as compared to the initial fluid dynamics value, and that the relative mean error of the simulated inner diameter was less than 8%. The proposed study provides deeper insight into the printing of hollow fibers and other gelling processes which utilize a reactor-like spinneret.
The nanocomposites, consisting of BaFe12O19 ferrite and few-layer graphene sheets (FL-GSs) in various weight ratios (1−9 wt. %), were fabricated by a mechanical mixing method. The high-crystalline FL-GSs were prepared by direct current arc discharge evaporation of pure graphite electrodes in an H2–Ar gas mixture. We measured the electromagnetic properties, including effective magnetic permeability and effective permittivity in addition to microwave absorption performance, of the FL-GSs/BaFe12O19 nanocomposites compared with the pristine BaFe12O19 nanoparticles (NPs). The nanocomposite FL-GSs/BaFe12O19 with the optimal performance (6 wt. % FL-GSs) exhibited an effective microwave absorption (<−10 dB) bandwidth of 5.8 GHz with a thickness of 2.2 mm, 53% higher than that of the pristine BaFe12O19 NPs. Meanwhile, this nanocomposite had the minimum reflection loss of −49.7 dB at 8.4 GHz with a thickness of 2.8 mm, three times greater than those without FL-GSs. These performances result from a simultaneous increase in both magnetic and dielectric losses possibly due to synergistic effects of BaFe12O19 and FL-GSs. In such nanocomposites, both magnetic loss from BaFe12O19 and dielectric loss from FL-GSs contribute to the absorbing performances. Adding FL-GSs as dielectric fillers enhances the impedance matching of the nanocomposites compared with the pristine BaFe12O19 NPs based on the magnetic loss alone. Our results indicate that the incorporation of high-crystalline nanocarbon materials into ferrite oxides can provide high microwave absorption intensity and broad effective absorption bandwidth, while maintaining high thermal stability.
The electromagnetism and microwave absorption properties were investigated in the frequency range of 2–18 GHz for the nanocomposites NiCo-SWCNTs/CoFe2O4 consisting of Ni-Co attached single-walled carbon nanotubes (NiCo-SWCNTs) and CoFe2O4 nanocrystals with different ingredient weight ratios. NiCo-SWCNTs were mass-produced by a direct current arc discharge in helium and CoFe2O4 was synthesized by a sol-gel method. Premium microwave absorption properties (mainly in Ku-band, i.e., 12–18 GHz) were obtained due to the appropriate combination of the complex permeability and permittivity resulting from the magnetic nanocrystals and high-crystalline NiCo-SWCNTs. The NiCo-SWCNTs/CoFe2O4 nanocomposites with 15 wt. % NiCo-SWCNTs exhibited the best microwave absorption property, whose reflection loss (RL) value reached −47.9 dB at 14.7 GHz and the absorption bandwidth (RL<−10 dB) was up to 7.1 GHz (from 10.5 to 17.6 GHz) with a matching thickness of only 1.8 mm. Our results indicate that the studied nanocomposite could be used as a promising candidate for lightweight microwave absorption materials.
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