Study On The Melting-Sintering-Rheological Characteristics Of Zhundong Coal Ash

Burning of Zhundong coal caused many problems,such as ash and slagging.Although coal blending can alleviate the delayed slag deposition process of Zhundong coal ash in the boiler,it cannot eliminate the problem of boiler slagging.The liquid slag boiler provides a new idea for Zhundong coal utilization.The liquid slagging boiler requires that the ash slag is smoothly discharged from the boiler in the form of liquid slag,and the high-temperature liquid ash slag cannot corrode and scour the refractory in liquid slagging boiler.Therefore,it is of great significance to study the mineral conversion and phase transformation process,sintering characteristics and ash flow characteristics of Zhundong coal ash at high temperature.Firstly,TG-DSC,XRF,XRD and FSEM-EDS were applied to study mineral conversion in Zhundong coal.The results show that minerals always change towards diversification at high temperatures;sodium-containing minerals cannot coexist in multiple ways,so as the temperature rises,all sodium-containing minerals have to transform.The process of mineral change is accompanied by phase change,so sodium can greatly reduce the melting temperature of coal ash and aggravate the tendency of coal ash contamination.Iron minerals have a significant effect on the evolution of sulfur-containing minerals,Fe₂O₃ in the ash promotes the decomposition of anhydrite and inhibits the decomposition of hauyne.Then,the sintering characteristics of Zhundong coal ash and refractory was studied bythe same method as described above.The results show that the characteristic temperature for sintering of refractory materials and coal ash is approximately 1100?.Refractory materials promote the melting of quartz and gehlenite in coal ash,which is the sintering mechanism of coal ash and refractory materials.Sintered slag can protect the refractory materials.But if the temperature is higher than 1200?,refractories will oxidize.The concept of limit thermal load was proposed in order to evaluate the high-temperature chemical stability of refractory materials.Zhundong coal ash significantly reduced the limit heat load of refractory materials during the sintering reaction.Finally,the high-temperature flow characteristics of Zhundong coal ash slag was studied using high temperature viscometer,together with ash melting point analyzer,XRF and FSEM-EDS.And prediction model of Zhundong coal slag viscosity was established.The results show that Zhundong coal ash slag has a low viscosity at high temperatures and is suitable for liquid slagging boilers.A large amount of sulfur minerals and residual carbon in ash slag will cause the jitter of viscosity,which is unfavorable for the operation of liquid slagging boilers.The prediction model of Zhundong coal ash slag viscosity is consistent with the experimental results of viscosity measurement,and can accurately reflect the high temperature flow characteristics of Zhundong coal ash slag,especially for the minimum operating temperature of the liquid slag boiler(corresponding to the temperature of 25Pa·S viscosity)The predicted value is close to the experimental result.