Analysis and Evaluation of Ash Deposits from the Coal-Fired Callide Oxyfuel Project

摘要

After the close of the Callide Oxyfuel Project, mature deposit samples were collected from the primary and secondary superheater tubes. These samples were studied with the aim of providing a description of deposits from an industry scale oxy-fuel plant and to gain some understanding of the deposition mechanism involved in their formation. The deposits formed over a 3 year operating period, with both air and (more extensive) oxy-firing, including many air-to-oxy transitions, boiler starts and trips, and fired predominantly by a coal with Fe2O3 in ash analysis of about 10%. The mineral character of the coal is relatively simple with silicon and aluminum clays and silica and iron-containing siderite dominant. This character allows for the plotting of chemical analysis results in triangular phase diagrams used to interpret scanning electron microscopy with energy-dispersive X-ray spectroscopy analysis, with iron being associated with the slagging mechanisms. The deposits were unusual in that layers of iron-rich particles and alumina silicates formed 10-50 mu m from the interface with the metal tubes, running parallel to the direction of deposit growth and normal to the tube surface, showing that deposition of each layer occurs concurrently.