Abstract
The application of circulating fluidized bed technology in calcium looping (CaL) requires that CaO-based sorbents should be manufactured in the form of spherical pellets. However, the pelletization of powdered sorbents is always hampered by the problem that the mechanical strength of sorbents is improved at the cost of loss in CO2 sorption performance. To promote both the CO2 sorption and anti-attrition performance, in this work, four kinds of pore-forming materials were screened and utilized to prepare sorbent pellets via the extrusion-spheronization process. In addition, impacts of the additional content of pore-forming material and their particle sizes were also investigated comprehensively. It was found that the addition of 5 wt.% polyethylene possesses the highest CO2 capture capacity (0.155 g-CO2/g-sorbent in the 25th cycle) and mechanical performance of 4.0 N after high-temperature calcination, which were about 14% higher and 25% improved, compared to pure calcium hydrate pellets. The smaller particle size of pore-forming material was observed to lead to a better performance in CO2 sorption, while for mechanical performance, there was an optimal size for the pore-former used.
Highlights
Greenhouse gases, such as CO2 which is mainly produced from fossil fuel combustion, are believed to be the major contributors to the rise of global temperatures [1]
Calcium hydroxide (CH)-PE5 from from the the mass fraction results, which is the highest. These results indicate that the addition of a small amount mass fraction results, which is the highest. These results indicate that the addition of a small amount pore-formers pore-formers enhances enhances the the mechanical mechanical strength strength of of sorbent sorbent pellets
It was found that the addition of PE had a positive effect on enhancing the CO2 sorption capacity maintaining a relatively high mechanical strength, compared to pure Ca(OH)2 pellets
Summary
Greenhouse gases, such as CO2 which is mainly produced from fossil fuel combustion, are believed to be the major contributors to the rise of global temperatures [1]. CO2 is captured in a carbonator at around 650 ◦ C by CaO-based sorbents and released subsequently in a calciner above 900 ◦ C In this way, CO2 in the flue gas can be separated and collected in high purity. All the natural sorbents will face a severe problem of loss-in-capacity due to sintering at a high temperature [11,12]. In order to obtain sorbent pellets with balanced mechanical and chemical performance, in this work, the pore-forming materials, widely used in industry, including polyethylene, polystyrene, graphite, and microcrystalline cellulose were screened and tested by the fabrication of CaO-based sorbent pellets using an extrusion-spheronization method. The effects of different pore-forming materials, their size, and doping ratio were comprehensively investigated and evaluated, and the roles of pore-forming materials in the preparation of sorbent pellets were well understood
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