Influence of inert solid binder for CaO based carbon capture

“It was hypothesised that the presence of an inert solid binder would improve the long-term carrying capacity by decreasing the rate of sintering (as well as improving the mechanical stability–discussed below with reference to the BFB experimental results). The extent by which the presence of binder reduces the rate of sintering is shown in Figure 2a which compares the decay in conversion (X) through 30 cycles for the synthetic sorbent with binder loading from 0–25 %. The performance of a natural limestone (Havelock) is also shown as a benchmark. An optimal binder loading of 15 % was observed; increasing the amount of binder to 25 % led to a decrease in the long-term conversion and no significant improvement (within the range of experimental variability) is observed with a binder loading of 5 %, compared to the pure PCC.
The decay profile through for the synthetic sorbent in the first 3–4 cycles follows a different trajectory compared to the natural limestone and the PCC owing to the formation of the mixed Ca-Al oxide. There is a trade-off because as the amount of binder is increased there is a corresponding decrease in the amount of reactive CaO. Hence, in Figure 2b, we compare the carrying capacity expressed in terms of g-CO2 per g-of calcined sorbent, clearly showing the superior carrying capacity of the synthetic sorbent (about three times the capacity of the natural limestone after 30 cycles). An optimal binder loading of about 15 wt.% is consistent with the
literature [12–15].”


“Figure 2. Carrying capacity through 30 CO2 capture-and-release cycles of synthetic CaO-based sorbents with binder loading from 0-25 wt. % and compared with natural limestone (Havelock), expressed in terms of: (a) conversion, X; and (b) g-CO2 per g-calcined sorbent ”

“As mentioned above, it was hypothesized that the presence of the binder would improve the mechanical stability of the sorbent and that synthetic sorbent with larger amounts of binder would be most resistant to attrition and decrepitation. Surprisingly, experimental results conducted in the BFB showed a decrease in the carrying capacity at 15 cycles corresponding
with an increase in binder loading from 0–25 % (Figure3a). The decrease in capacity was coupled with an increase in the amount of bed material lost owing to elutriation from 3 % to 15 % after 15 cycles, for PCC with no binder and synthetic sorbent with 25 wt.% binder, respectively. Figure 3b compares TGA with BFB results with the latter data set also given with a correction made for mass loss. In the case of the 85 % CaO it is clear that the difference in the carrying capacity is not solely due to the loss of reactive material. The dramatic decrease in the capture capacity of the CaO with binder from the TGA to BFB suggests that the structural changes during the solid-state mixed oxide reaction are very significant in terms of the subsequent reactivity of the sorbent.”


“Figure 3. (a) Carrying capacity of CaO with varying amounts of binder and compared with Havelock in a bench-scale BFB; (b) Comparison between BFB and TGA with BFB results corrected for mass loss owing to elutriation of fine particles”


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