Mechanism And Fuzzing Judge Of Ash Slagging On Refractory Lined On Water-wall Of Coal-fired Boilers

The ash content of coal for our country coal-fired boilers commonly is high and low with heat value and volatility. In order to improve the ignition , stable combustion and burning-out ability of inferior coal, the coal-fired boiler has widely adopt fire-resistant liner, while, the slagging problem of molten coal ash on the fire-resistant liner appears, which can change the combustion aerodynamic status in the furnace and the flue gas temperature at hearth export, then change heat transfer of vapour and water of boilers. It affects stable operation of boiler, leads to the sfe accident of boiler even. Be to lighten and avoid slagging on the fire-resistant liner, it is necessary to fully study molten ash deposition and slagging mechanism with refractory material and follow to make reasonably judgment for slagging extent. There has an important practical significance to rationally choice and design refractory material of liner, adjust and improve coal combustion and ensure safely and effective operation of coal-fired boilers.This dissertation relies on the project of molten coal ash sediment mechanism and action on refractory material supported by the national natural science foundation, firstly through static erosion experiments of molten coal ash on the refractory material board in high temperature muffle analyzed the molten coal ash chemical reaction mechanism on the surface of refractory board, the diffusion and segregation mechanism of element compositions of coal ash and refractory board during eroding and slagging by microscopic methods. Secondly considering the influence of combustion status to slag during coal-pulverized torch burning, coal-pulverized torch simulation experiments in nozzles horizontal furnace were carried out, analyzed diffusion mechanism of sediment coal ash on refractory boards in different places of coal-pulverized torch. Lastly according to the serious slagging situation on fire-resistant liner in the furnace of tangential pulverized coal-fired boiler which have been widely applied in our country, the slagging test in Shimen power plant was carried out for eight months, it is more systematical and comprehensive to study the molten caol ash slagging mechanism on the refractory materials.The results of study about static erosion experiments indicate that selective segregation of element compositions is in favor of nucleation and crystallization for coal ash situated in the interface of coal ash and refractory board, and weakening the conglutination between coal ash and refractory board. Under oxidative atmosphere basic components of coal ash diffuses and erodes more easily in high aluminium fire-resistant board, the erosion velocity has increased by 0.09μm/(℃.h) within the temperature range of 1350℃-1500℃in the furnace with the ratio of basic components to acid components in coal ash increasing to 0.174 from 0.053.The results of study about ash slag sediment, components diffusion and micro-phases transformation in coal-pulverized torch show that basic components are propitious to nucleation and crystallization for alumina refractory board but SiC, and easily aggrade on the surface of SiC refractory board. Alumina in coal is propitious to nucleation and crystallization for SiC refractory material.The results of microcosmic analysis for sediment slag samples on the fire-resistant liner of boiler in power plant show that there is not obvious erosion to SiC refractory board and the main phases of sedimentary slag layer are all kinds of complex crystal transformed by basic components, and exists selective segregation of element compositions on the interface of ash slag and SiC refractory board. This meeting validates the rationality of the analysis about the slagging mechanism too.The results of experiment study show too that the conglutination extent between molten coal ash and refractory board has consanguineous relation to the crystallinity of ash slag on the interface of ash slag and refractory board. The conglutination extent will weaken if the crystallinity increases. Generally when the crystallinity is less than 30% , the serious slagging will occur, after more than 70% and slagging slightly. Alumina fire-resistant liner adapts to the boiler combusting the coal with more basic components content of it's ash, and SiC fire-resistant liner adapts to the initial burning section with low combustion temperature and strong reducing atmosphere of the coal-fired boiler.At last, based on the molten coal ash slagging mechanism on refractory board, combining the crystallinity of coal ash slag on the interface of ash slag and refractory board, the slagging content on the fire-resistant material can be judged by fuzzy mathematics. It can comprehensively reflect the molten coal ash slagging content on the fire-resistant, and can give an accurate mathematic describe, avoid the illegibility of judge of slagging extent.