Abstract
The Ash Fusion Test (AFT) is considered to be the most popular method of characterising the melt characteristics of solid fuel ash. This study shows how pellet preparation can make significant improvements to repeatability. Pelleting pressure, pellet particle size, pellet shape, and furnace ramp rate were investigated to establish the most repeatable representation of ash melting relevant to pulverised fuel combustion in a furnace in an oxidizing atmosphere up to 1600 °C. A 5 mm machine pressed pellet was found to produce the best results as it identified the earliest initial deformation temperature (IDT), gave the least error, and displayed the greatest visible change in pellet height to enable easy identification. Reducing maximum ash particle size to <72 µm and increasing the pressure of the pelleting process was also shown to produce a 120 °C reduction in the IDT when compared with other methods. Reducing the ashing temperature and retaining volatiles lost during high temperature ashing were shown to have a negligible impact on IDT. The characteristic AFT curve was also used to quantify the extent of shrinkage and swelling during the test.
Highlights
Slagging and fouling are key issues for the power industry and cause significant problems with continuous, long term boiler operation [1,2]
Each sample was run in triplicate, with the average displayed on the Advanced ash fusion test (AAFT) plot
The composition of the samples is given by moisture, Kellingley coal ash has been pelleted using a range of different methods and tested in the Carbolite Gero CAF G5 furnace
Summary
Slagging and fouling are key issues for the power industry and cause significant problems with continuous, long term boiler operation [1,2]. The AFT was developed in the early days of the power industry to predict clinker (large lumps of ash) forming characteristics in stoker furnaces [16]. It continues to be used, with minimal changes to the methodology since its inception in the early 1900s [16]. The current method of preparing samples for the AFT relies on hand-made cones or cylinders of ash, combined with a binder, and sometimes with the use of a hand press. Further to the empirical tests, multiple predictive methods are documented [9,13,14,22,23,24,25]. A more recent review correlates sticking probability to ash fusion temperatures alongside other modelling techniques [26]
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