Study On The Effect Of Coal Ash Deposition On The Coal Combustion Reactor

To comprehensively understand and solve the ash and slag deposition and agglomeration problems in coal combustion process, we need make clearly not only the fundamental properties of coal ash and slag but also the interactions among each components; especially the relations between components and micro-structures at an extra high temperature. In this thesis, the works were carried out step-by-step to explore these complicate behaviors of ash and slag. Systematically, temperature-dependent mineral and structural transitions of ashes were examined from various aspects to identify the general characteristics of coal ash transformation. The conclusion relating to the structures and molten properties of several coal ashes in the respective chapters is summarized as follows.Compositional and structural transformations of ash were compared to its melting behavior. The following conclusions were obtained:1) low-temperature ash contained quartz and clays (such as kaolinite). Continuous transition and reaction of silica and alumina around1200℃accelerated softening of the ash;2) a liquid phase as an amorphous glass was mainly formed by the silica and mullite eutectic solution at about1400℃;3) fine solid particles of alumina appeared in the molten ash, probably derived from kaolinite, and solid particles in the molten ash with a variety of frameworks.The reaction between the primary compositions in this system, especially, the interactions among iron oxides and calcium oxide were investigated. Results demonstrate that, CaO and iron oxide both are valuable fluxing agents. Iron reduced to metallic will increase the viscosity quite obvious. Iron oxide, Fe2O3, may take part in the random glass network in a fashion similar to aluminum oxide. And also, it is found that CaO enhanced the soluble ability of iron oxides in the SiO2-Al2O3-CaO-FeOx quaternary system.Low melting point ash evaporated and formed spherical particle after cooling. Depend on their size, ash particles may entrained to filters or remains in the bed. Particle size distribution and compositions of fly ash and temperature in the filters contribute to the difficulty in the removal of fly ash and fluctuation of pressure drop across a filter system.