Browsing by Author "Yu, Zhijian"
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Item Open Access Attrition study of cement-supported biomass-activated calcium sorbents for CO2 capture(American Chemical Society, 2016-08-19) Duan, Lunbo; Yu, Zhijian; Erans Moreno, Maria; Li, Yingjie; Manovic, Vasilije; Anthony, Edward J.Enhanced CO2 capacity of biomass modified Ca-based sorbent has been reported recently, but undesired attrition resistance has also been observed. Cement was used as a support for biomass-activated calcium sorbent during the granulation process in this study, in order to improve the poor mechanical resistance. Attrition tests were carried out in an apparatus focused on impact breakage to evaluate how the biomass addition and cement support influence the particle strength during Ca-looping. Results showed biomass addition impaired the mechanical strength and cement support could improve it, which is reflected by the breakage probability and size change after impact of pellets experienced calcination and multiple calcination/carbonation cycles. Larger-sized particles suffered more intense attrition. The mechanical strength of sorbents declined significantly after higher temperature calcination but increased after carbonation. After multiple cycles, the mechanical strength of particles was greatly enhanced, but more cracks emerged. A semi-empirical formula for calculating average diameter after attrition based on Rittinger’s surface theory was developed. Observation on the morphology of particles indicated that particles with more porosity and cracks were more prone to breakage.Item Open Access Effect of steam hydration on reactivity and strength of cement-supported calcium sorbents for CO2 capture(Wiley, 2017-05-23) Yu, Zhijian; Duan, Lunbo; Su, Chenglin; Li, Yingjie; Anthony, Edward J.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.