Tinkham, Kevin Michael (1989) Surface studies of pulverized fuel ash. University of Southampton, Doctoral Thesis.
Abstract
The tendency for pulverized fuel ash (PFA) to be retained on heat transfer surfaces located within coal-fired power station boilers is responsible for several operational difficulties experienced in electricity generation. The mechanisms of ash formation and transport are quite well understood but the factors which lead to ash retention are not. It is believed that the surface composition of ash particles must play a major role in determining their ability to adhere to heat transfer tubes. In order to investigate the outermost regions of ash particles, a series of surface spectroscopic analyses have been carried out, the results and interpretation of which constitute the bulk of the work presented in this thesis. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) have been used in conjunction with energy dispersive X-ray (EDX) analysis to provide information about the distribution and chemical nature of elements within a range of PFA samples. In addition, both AES and SIMS were employed to analyze individual particles, thereby establishing that single particles may have a very different composition from the average obtained for a particular ash. Mossbauer spectroscopy has been used to examine the nature of iron within PFA and a preliminary investigation, using XPS, has also been undertaken into the oxidation in air of heated pyrite, a mineral which has long been implicated in the process of boiler fouling. As a result of these investigations, significant chemical information on a number of elements and trends in their distribution profiles within PFA have been obtained. The findings have been used to examine some fundamental aspects of ash formation and the tendency of ash to adhere to heat transfer surfaces.
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