Study On The Mineral Transformation And The Slagging Characteristic During Coal Combustion

The slagging of power plants not only make economic losses,but also be harm to the security of power plant,which can decrease the boiler's heat-transfer capacity ,increase the resistance of flue and break the water-cooled hopper when slag fell. The coal minerals become ash and stick to the heat exchange surface in combustion.So it is important to study the transformation of minerals in coal combustion and the mechanism of slagging.Five common coals and power plant coals were selected and made their Low temperature ash(LTA) and high temperature ash .Analysis their minerals and slagging index. The LTA can keep the original minerals of coals,which contain clay minerals, oxide, sulfate and sulfide, carbonate, and other minerals. The ash melting based on the quality of minerals. The experiment result show boehmite ,kaolinite and rutile are refractory mineral , and iron mineral, Ca-mineral and quartz companied by Fe or Ca are easily melt .Generally, the more complex the mineral are ,the more easy to melt.The mineral transformation in oxygenic environment are concluded. And Ca-Mg silicate, garnet and feldspar were detected in the ash when close to be melt. Most of the iron mineral transform into iron oxide, indicates the iron mineral have no melting effect in oxygenic environment. And the thermal-gravity curves of the LTA were analyzed to detect the thermal behavior of the minerals, the mass loss curve and the endothermal curve change as the minerals.Slag on the refractory belt from Guile power plant was collected and detected by XRD and ESEM, which is a fused iron slag rich in Fe and Si composition. Each layer contains plenty of grass phase , and the main minerals are hematite , quartz and iron oxide. The quadrate crystals are hematite and the needle-like mineral are Fe aluminosilicate such as hematite and Fe spinel.At last,the power plant slag is classified into fused slag and sintered slag depending on the fused degree, and are divided into Fe ,Ca and Fe-Ca slag based on the composition. Finally ,the mechanism of ash deposits and the development of mathematic models of slagging were summarized.