Enrichment of heavy metals during coal combustion by mineral additives

Experiences of pulverized coal combustion with different mineral additives were carried out in a tube furnace. When the mass addition ratio of the four mineral additives (Kaolin, montmorillonite, attapulgite and limestone) were 0, 1%, 3% and 5%, the enrichment effects of heavy metals (Pb, Cd, Zn and Cr) were studied at 900-1300℃. The results indicate that there exists a positive correlation between the addition of additives and the retention rate of each heavy metal, and the addition ratio of 5% is more suitable. The suitable enrichment temperature range of the additives for Pb and Cd is 900-1000℃. The retention rates of Pb and Cd are maintained at approximately 60% in this temperature range. The suitable temperature for Zn enrichment is 900℃. The retention rate of Zn is close to 70% at this temperature. The temperature range for Cr is 1000-1100℃, and the retention rate of Cr can reach 82. 1%. When the temperature reaches 1100℃, the coking of coal ash will lead to a decrease in the retention rate of the four heavy metals. When the temperature rises to 1200℃, the retention rate will drop significantly;the additives are almost completely inactivated at 1300℃; and among them, the retention of Pb is only about 25%, the retention of Cd and Zn is reduced to approximately 30%, and the retention of Cr is reduced to 56% or less. Comparing the enrichment effects of the four additives on Pb, Cd, Zn and Cr, Kaolin and attapulgite have better performance, followed by montmorillonite and limestone is the last. This study can provide theoretical and experimental basis for pollution control of heavy metals in coal-fired power plants. © 2020, Chemical Industry Press. All right reserved.