Unconventional inorganic characteristics of 4 types of Xinjiang coals and their influence on the generation of ultrafine particles

A deep understanding of the effects of the inorganic characteristics of Xinjiang coals on combustion particulate generation is of great significance for their clean and efficient utilization. This work investigated the inorganic characteristics of Wucaiwan coal (WCW), Wanxiang coal (WX), Tianchi coal (TC), and Xiheishan coal (XHS) and the their relationship with the production of ultrafine particulates during combustion. The results show that the four Xinjiang coals are mainly lignites with low ash and sulfur contents. Coal ashes are enriched in basic elements. Among them, the content of Na₂O (3.58%−7.13%) is commonly higher than that of conventional utility coals. The ashes of WCW and WX coals have higher contents of CaO (> 33%), but low contents of SiO₂ and Al₂O₃. WX coal is particularly characterized by high Na and Cl. The Na in coal is primarily water soluble(62.3%−90.6%). The K is mainly HCl insoluble. The Fe occurs primarily as HCl soluble and insoluble forms. And the distribution of Ca and Mg in different forms varies according to coal types. The composition of ultrafine particulate matter from Xinjiang coal combustion is dominated by Na, K, Cl, and S. The particle size range of the ultrafine particulate matter is accurately defined by using the condition that the mass fraction of Na₂O+K₂O+Cl+SO₃ is higher than 50%. The ultrafine particulate matter of WCW, TC and XHS coals has similar particle size ranges (≤0.07 μm); while the ultrafine particulate matter of WX coal, which has the highest content of Na in the water-soluble form, has a wider particle size range (≤0.76 μm). The generation of ultrafine particulate matter (y) is found to be highly linearly and positively correlated with the total amount of water-soluble (Na+K) (x) in the coal, with the relationship equation y = 0.528x−0.239 and the correlation coefficient of 0.948.