100 research outputs found

    CO2 capture and attrition performance of competitive eco-friendly calcium-based pellets in fluidized bed

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    A system incorporating spent bleaching clay (SBC) into the calcium looping (CaL) process has been proposed. In this paper, prepared sorbents doped with regenerated SBC and cement were tested in a bubbling fluidized bed (BFB) to examine in detail their cyclic CO2 capture capacity and attrition properties. The results revealed that the cyclic CO2 capture capacity of pellets modified by pyrolyzed SBC and/or cement showed significantly better performance than limestone, which is consistent with the thermogravimetric analyzer (TGA) results. This is due to the improvement of pore structure and enhanced sintering resistance created by adding support materials to the sorbent. The elutriation rates of the composites prepared with pyrolyzed SBC and/or cement were consistently lower than for crushed limestone. Scanning electron microscopy (SEM) images indicated that the pellets possessed higher sphericity than limestone particles, thus reducing surface abrasion. Limestone exhibited a high attrition rate (diameter reduction rate) of 10.7 μm/cycle, which could be eliminated effectively by adding regenerated SBC and/or cement. ‘L‐5PC‐10CA’ (85% lime/5% pyrolyzed SBC/10% cement) exhibited an attrition rate of only 7.9 μm/cycle. Based on the analysis of breakage and probability density function (PDF) for particle size distribution, it appeared that pellets without cement experienced breakage (mostly chipping and disintegration) and surface abrasion, whereas ‘L‐10CA’ (90% lime/10% cement) and ‘L‐5PC‐10CA’ mainly suffered surface abrasion, combined with some chipping

    From waste to high value utilization of spent bleaching clay in synthesizing high-performance calcium-based sorbent for CO 2 capture

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    A novel calcium looping (CaL) process integrated with a spent bleaching clay (SBC) treatment is proposed whereby fuels and/or heat from regeneration of SBC provide extra energy for the calcination process, in addition, the regenerated SBC can be used to synthesize enhanced CaO-based sorbents. Different kinds of composite samples were prepared with the regenerated SBC and/or aluminate cement at various doping ratios via a pelletization process. All pellets were subjected to thermogravimetic analyzer tests employing severe reaction conditions to determine the optimal doping ratios and regeneration method for the SBC based sorbents. These results demonstrate that pellets containing combustible components showed higher CO2 uptakes, due to the improved pore structure, which was verified by N2 adsorption measurements. The as-prepared sorbent “L-10PC” (90 wt.% CaO/10 wt.% pyrolytic SBC) achieved a final CO2 uptake of 0.164 g(CO2) g(calcined sorbent)−1 after 20 cycles, which was 67.3% higher than that of natural limestone particle. A new larnite (Ca2SiO4) phase was detected by X-ray diffraction analysis, however the weak diffraction peak associated with it indicated a low content of larnite in the pellets, which produced a smaller effect on performance compared to cement. A synergistic effect was achieved for a sample designated as “L-5PC-10CA” (85 wt.% CaO/5 wt.% pyrolytic SBC /10 wt.% cement), which resulted in the highest final uptake of 0.208 g(CO2) g(calcined sorbent)−1 after 20 cycles. Considering the simplicity of pyrolysis regeneration process and the excellent capture capability of pellets doped by pyrolytic SBC, the proposed system integrating CaL with SBC pyrolysis treatment appears to offer particular promise for further development

    Traction Power Substation Load Analysis with Various Train Operating Styles and Substation Fault Modes

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    Simulation of railway systems plays a key role in designing the traction power supply 13 network, managing the train operation and making changes of timetables. Various simulation 14 technologies have been developed to study the railway traction power network and train operation 15 independently. However, the inter-action among load performance, train operation and fault 16 conditions have been fully understood. This paper proposes a mathematical modeling method to 17 simulate the railway traction power network with consideration of multi-train operation, driving 18 controls, under-voltage traction, and substation fault modes. The network voltage, power load 19 demands, energy consumption according to the existing operation are studied. The hotspots of the 20 power supply network are identified based on the evaluation of train operation and power demand. 21 The impact of traction power substation (TPSS) outage and short circuit on the power supply 22 network have been simulated and analyzed. The simulation results have been analyzed and 23 compared with the normal operation. A case study based on a practical metro line in Singapore 24 Metro is developed to illustrate the power network evaluation performance

    Magnetic anisotropy in hole-doped superconducting Ba 0.67K 0.33Fe 2As2 probed by polarized inelastic neutron scattering

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    We use polarized inelastic neutron scattering (INS) to study spin excitations of optimally hole-doped superconductor Ba0.67_{0.67}K0.33_{0.33}Fe2_2As2_{2} (Tc=38T_c=38 K). In the normal state, the imaginary part of the dynamic susceptibility, χ(Q,ω)\chi^{\prime\prime}(Q,\omega), shows magnetic anisotropy for energies below \sim7 meV with c-axis polarized spin excitations larger than that of the in-plane component. Upon entering into the superconducting state, previous unpolarized INS experiments have shown that spin gaps at \sim5 and 0.75 meV open at wave vectors Q=(0.5,0.5,0)Q=(0.5,0.5,0) and (0.5,0.5,1)(0.5,0.5,1), respectively, with a broad neutron spin resonance at Er=15E_r=15 meV. Our neutron polarization analysis reveals that the large difference in spin gaps is purely due to different spin gaps in the c-axis and in-plane polarized spin excitations, resulting resonance with different energy widths for the c-axis and in-plane spin excitations. The observation of spin anisotropy in both opitmally electron and hole-doped BaFe2_2As2_2 is due to their proximity to the AF ordered BaFe2_2As2_2 where spin anisotropy exists below TNT_N.Comment: 5 pages, 4 figure

    Effect of steam hydration on reactivity and strength of cement-supported calcium sorbents for CO2 capture

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    Steam hydration was used to reactivate spent cement-supported CO2 sorbent pellets for recycle and the effect of steam hydration on the reactivity of sorbents was investigated in a bubbling fluidised reactor. A specially designed impact apparatus was developed to evaluate the strength of the reactivated pellets as well as determine the effect of “superheating”. It was found that the reactivity of synthetic pellets was significantly elevated over that of raw limestone after steam hydration. The CaO conversion of spent pellets increased from 0.113 to 0.419 after hydration, whereas that of spent limestone ranged from 0.089 to 0.278. The CaO conversions of hydrated samples calcined under different conditions achieved the identical level, proportional to the degree of hydration. As expected, the mechanical strength of synthetic pellets declined severely after reactivation. Large cracks emerged on hydrated limestone as seen in scanning electron microscope images. By contrast, similar cracks were not observed for synthetic pellets after hydration, although hydration did produce higher porosity than seen with limestone and an increased surface area, which enhanced CO2 capacity and was associated with an increase in strength loss. The breakage rate of superheated steam-reactivated limestone derived pellets was about half that of hydrated samples. This demonstrates that superheating treatment (which allows the annealing of stacking faults and mechanical strain produced by hydration) enhances the strength of hydrated pellets. This work demonstrated that combining steam hydration with superheating can both reactivate the spent synthetic pellets and reduce strength decay associated with the hydration process

    CO2 capture performance using biomass-templated cement-supported limestone pellets

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    Synthetic biomass-templated cement-supported CaO-based sorbents were produced by granulation process for high-temperature post-combustion CO2 capture. Commercial flour was used as the biomass and served as a templating agent. The investigation of porosity showed that the pellets with biomass or cement resulted in enhancement of porosity. Four types of sorbents containing varying proportions of biomass and cement were subject to 20 cycles in a TGA under different calcination conditions. After first series of tests calcined at 850 °C in 100% N2, all composite sorbents clearly exhibited higher CO2 capture activity compared to untreated limestone with exception of sorbents doped by seawater. The biomass-templated cement-supported pellets exhibited the highest CO2 capture level of 46.5% relative to 20.8% for raw limestone after 20 cycles. However, the observed enhancement in performance was substantially reduced under 950 °C calcination condition. Considering the fact that both sorbents supported by cement exhibited relatively high conversion with a maximum value of 19.5%, cement promoted sorbents appear to be better at resisting of harsh calcination conditions. Although flour as biomass-templated material generated significantly enhancement in CO2 capture capacity, further exploration must be carried out to find the way of maintaining outstanding performance for CaO-based sorbents under severe reaction conditions