Lin Kunsen, Zhao Youcai, Kuo Jia-Hong, Lin Chiou-Liang
The State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
Department of Safety, Health and Environmental Engineering, National United University, 36063 Miaoli, Taiwan.
Sci Total Environ. 2023 Feb 1;858(Pt 1):159759. doi: 10.1016/j.scitotenv.2022.159759. Epub 2022 Oct 27.
Phosphorus and operating temperature not only affect the agglomeration behavior but also the transformation and migration of heavy metals. Accordingly, this study examined the effect of temperature and phosphorus in a fluidized bed combustion process to understand the emission and distribution of heavy metals by both experimental and thermodynamic calculations. The experimental results indicated that the sodium-phosphate reactions occur before the sodium-silicate reaction in the solid phase when the ratio of P/Na was 1/2. A low-melting-point sodium phosphate component, such as NaPO leads to easier particle agglomeration than NaO-SiO. In terms of the emissions of heavy metals, Pb and Cd show a similar trend: both the amount of emission smaller than that without adding phosphorus and the amount of emission share an upward trend with the operating time increased during MSS fluidized bed combustion. However, with the presence of phosphorus, the emission of Cr shows slightly decreased, and then sharply dropped, after that, increasing with operating time increased. Generally speaking, the maximum amount of Pb and Cd emitted was at 900 °C, followed by 800 °C and 700 °C. The higher temperature would promote the volatilization of Pb and Cd to emit. On the other hand, Cr emitted at the beginning tended to increase but later decreases when the temperatures were 700 and 900 °C, which may be due to the emission of Cr being influenced by the different affinities of both Al and Cr, reacting with Na in a fluidized bed incinerator. As for the distribution of heavy metals in the solid phase, a higher concentration of heavy metals was found in both the coarsest and finest particles during the process of agglomeration/defluidization.
磷和运行温度不仅会影响团聚行为，还会影响重金属的转化和迁移。因此，本研究考察了流化床燃烧过程中温度和磷的影响，通过实验和热力学计算来了解重金属的排放和分布情况。实验结果表明，当P/Na比为1/2时，固相中的磷酸钠反应先于硅酸钠反应发生。低熔点的磷酸钠成分，如NaPO，比NaO-SiO更容易导致颗粒团聚。就重金属排放而言，Pb和Cd呈现相似趋势：在MSS流化床燃烧过程中，二者的排放量均小于不添加磷时的排放量，且排放量随运行时间增加呈上升趋势。然而，在有磷存在的情况下，Cr的排放先略有下降，然后急剧下降，之后又随运行时间增加而增加。一般来说，Pb和Cd的最大排放量出现在900℃，其次是800℃和700℃。较高的温度会促进Pb和Cd的挥发排放。另一方面，当温度为700℃和900℃时，Cr的初始排放量趋于增加，但随后减少，这可能是由于流化床焚烧炉中Al和Cr与Na的亲和力不同，影响了Cr 的排放。至于重金属在固相中 的分布，在团聚/失流过程中，最粗和最细颗粒中均发现了较高浓度的重金属。
