The Characteristic Of Minerals Partition In Coal And Its Effect On Slagging Of Boiler

Boiler slagging caused by mineral transformation is a serious problem to the safeoperation of power plants, this paper focus on mineral transformation and boiler slagging, itis expected to make better understanding about slagging mechanism from this study.The low temperature ash of 9 kinds of typical coals were collected to conduct sinkfloatexperiments,and systematic research of chemical and mineral characteristic of thesink-float ash from sink-float experimets were taken later;and then author analysed themineralogy chracteristic and formation mechanism of the slagging samples that sellectedfrom zhuzhou power palnt;Finally summarised the typical heavy minerals transformation incoal combustion progress and analysed their impact on boiler slagging.Sink-float experiment results showed that: the mineral phase of 9 kinds of lowtemperatureashes were basically consisted of quartz kaolinite pyrite and calciummineral.Float ash mineral composition was basically the same as low-temperature ash,however,slight changes in content.Mineral partition of sink ash was definitely differentfrom low-temperature ash,they were divided into iron-bearing minerals calcium-bearingminerals and impure mineral according to their composition.Iron-bearing minerals are themain minerals in sink ash,and calcium-bearing minerals are secondary minerals,few amountof impurities like quartz category minerals and kaolinite were also detected in sink ash.TheFESM-EDX results show that: large number of iron-bearing minerals which mainlycomposed of pyrite were indentified in sink ash,according to its morphology,pyrite can bedivided into 9 categories: flake pyrite,massive pyrite,strawberry spherical pyrite,sphericalpyrite,fine particle pyrite,cylindrical pyrite,crystal pyrite,pentagonal dodecahedronpyrite,floccule pyrite.Anhydrite who has cylindrical microstructure was also indentified insink ash,and small crystal particles were enriched in its smooth surface.Fluorite,anataseand K-feldspar were detected by FESM-EDX occasionally.Six deposits were collected from different positions of boiler in Zhuzhou Power Plantin China.The mineralogy chemical composition and microstructure of them weredetermined by X-ray diffraction spectrometry (XRD) X-ray fluorescence spectrometry (XRF) optical microscopy and field scanning electron microscopy equipped with energydispersive X-ray spectrometry (FSEM-EDX) respectively.The results show that: the depositis mainly composed of silica amorphous phases,the chemical compositions and mineralogyof different layers varied with each other.The identified minerals include mullitecristobalite hematitequartz keatite hercynite and anorthite.The silica-rich glass phases arederived from the volatilization-recondensation of SiO and the interaction betweenaluminosilicates and other minerals.Six types of crystals were identified in the deposits,including stripy crystal,partical crystal,diamond crystal,cubic crystal,cluster and clasticcrystal.The deposition of crystals as well as the following melting is the main reason for theporosity structure of deposit.Viscous SiO formed glass in high temperature together withthe reaction and low temperature eutectic between fine mineral particals are the mainreasons of slagging in zhouzhou power plant.Typical iron minerals,calcium minerals,clay minerals and quartz transformation duringcoal combustion process were summarized.The contribution of pyrite in slagging wasmainly attributed to the formation of partial oxidation melted intermediate phases and aseries of low-temperature melts which were formed from the interaction of SiO2 withiozites that formed in reducing atmosphere.The lime which was the decomposed productfrom calcium minerals would reduce ash melting point and viscosity, thus resulting inslagging.Quartz formed the amorphous phase in slags,and could easily be reduced to SiOvapor in high temperature,Vapor condensation in the surface of wall tube facilitated thedeposition of other particles.Combustion-generated amorphous Si-Al oxides from claymineral were easily interact with iron and calcium minerals to form ternary and quaternarylow-temperature melts,thus accelerating the integration of the other minerals.