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SUN ET AL .
stage are shown in Figure 10, and the obtained kinetic param- eters were presented in Table 2. As can be seen in Table 2, the PLM shows much better carbonation performance compared with the LM. The values of k and t crcs of the PLM are all higher than those of the LM during the same cycle. For example, the values of k and t crcs during the 1st cycle are respectively increased by 29.9% and 120% after prewash treatment. The values of k and t crcs of the PLM in the 15th cycle are 144% and 28.0% higher than those of the LM in the same cycle. In other words, the PLM shows faster carbonation rate and longer duration time in the chem- ical reaction controlled stage in the same cycle. Certainly, higher carbonation conversion can be achieved for the PLM during the chemical reaction controlled stage. The X u of the PLM in the 1st and 15th cycles is 2.64 and 3.65 times as those of the LM in the same cycle. If the LM cannot be reused effectively, the major dis- posal for LM is landfill. Simultaneously, the Cl in the LM will penetrate into the underground water and lead to serious pollution. Therefore, the Cl in the LM was hard to handle and should be heavily focused on. In this manuscript, the LM was proposed to be CO 2 sorbent in calcium looping process. A prewash process was raised to decrease the Cl in the LM. Not only the CO 2 capture capacity of the LM was enhanced after prewash process, the Cl in the LM was also transferred into the discharged water, in which the Cl can be removed in more convenient ways. Dechloridation equipment can be employed to remove most of the Cl in the discharged water. After that, the spent water can be sent to the nearby sewage treatment plant for fine treatment before discharged to the environment. In this research, 400 g deionized water was used for 100 g LM during the prewash process. When applied to the prac- tice, the deionized water can be replaced by the surface fresh- water or the collected rainwater. Also, intense agitation can also be employed to enhance the dissolution of the Cl into the water and decrease the needed water.
FIGURE 8 Pore volume distribution of calcined LM, CaCO 3, and Cl-doped CaCO 3 with a Cl/Ca molar ratio of 2:100 at the first cycle
FIGURE 9
Carbonation conversions and carbonation rates of the
PLM with carbonation time during different cycles
CaCO 3 . It indicates that the Cl can aggravate the sintering of the LM during the calcination at high temperature, leading to reduction of pores distributed in 10-100 nm, which have been proved to be beneficial to diffusion of CO 2 in the sorbent to react with CaO. 25 Therefore, it is predictable that reducing the Cl content in the LM can enhance its CO 2 capture capacity. 3.3 | Effect of prewash treatment on the carbonation kinetics of LM A prewash treatment process was proposed to decrease the Cl content in the LM. As shown in Table 1, the Cl content in the LM decreases dramatically after the prewash treatment process. The carbonation conversions and carbonation rates of the PLM with carbonation time during different cycles are shown in Figure 9. The fitting results of the carbonation process of the PLM during the chemical reaction controlled
FIGURE 10
Fitting results of the carbonation conversions of the
PLM during chemical reaction controlled stage in the 1st cycle
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