Migration and transformation of Pb,Cu,and Zn during co-combustion of high-chlorine-alkaline coal and Si/Al dominated coal

Shaerhu(SEH)coal is abundant in Xinjiang,China.The utilization of SEH suffers from severe ash deposition,slagging,and fouling problems due to its high-chlorine-alkaline characteristics.The co-combustion of high-alkaline coal and other type coals containing high Si/Al oxides has been proven to be a simple and effective method that will alleviate ash-related problems,but the risk of heavy metals(HMs)contamination in this process is nonnegligible.Hence,the volatilization rates and chemical speciation of Pb,Cu,and Zn in co-combusting SEH and a high Si/Al oxides coal,i.e.,Yuanbaoshan(YBS)coal were investigated in this study.The results showed that the addition of SEH increased the volatilization rates of Pb,Cu,and Zn during the co-combustion at 800℃from 23.70%,23.97%,and 34.98%to 82.31%,30.01%,and 44.03%,respectively,and promoted the extractable state of Cu and Zn.In addition,the interaction between SEH and YBS inhibited the formation of the Pb residue state.SEM-EDS mapping results showed that compared to Zn and Cu,the signal intensity of Pb was extremely weak in regions where some of the Si and Al signal distributions overlap.The DFT results indicated that the O atoms of the metakaolin(Al_(2)O_(3)·2SiO_(2))(001)surface were better bound to the Zn and Cu than Pb atoms after adsorption of the chlorinated HMs.These results contribute to a better understanding of the effects of high-alkaline coal blending combustion on Pb,Cu,and Zn migration and transformation.

NO_(x) and H_(2)S formation in the reductive zone of air-staged combustion of pulverized blended coals

Low NO_(x) combustion of blended coals is widely used in coal-fired boilers in China to control NO_(x) emission;thus,it is necessary to understand the formation mechanism of NO_(x) and H2S during the combustion of blended coals.This paper focused on the investigation of reductive gases in the formation of NO_(x) and H2S in the reductive zone of blended coals during combustion.Experiments with Zhundong(ZD)and Commercial(GE)coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200℃–1400℃with an excessive air ratio of 0.6–1.2.The coal conversion and formation characteristics of CO,H_(2)S,and NO_(x) in the fuelrich zone were carefully studied under different experimental conditions for different blend ratios.Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H2S as NO reduction accelerated.Both the CO and H2S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio.Based on accumulated experimental data,one interesting finding was that NO and H2S from blended coal combustion were almost directly dependent on the CO concentration,and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus,CO,NO_(x),and H2S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.