A 9 wt.% Cr creep resistant power plant steel, P91, was subjected to transmission electron microscopy, energy dispersive x-ray and optical analysis in order to identify a method that may be used to assess the thermal history of the steel and to identify material which may have been subjected to incorrect pre-service heat treatment. As a first step, the relatively simple technique of optical image analysis was used. Photographs of etched ex-plant P91 specimens were analysed using an automated optical image analyser in order to identify any apparent trends that may be used as an indicator to either the service history or the pre-service heat treatment of the steel. The main parameter used was the amount of black space on each image, itself a function of both precipitation within the material and etching procedure. This technique provided inconsistent results due to the inherent problems in creating reproducible images and sensitivity.

Slagging and fouling during the combustion of pulverised coal in boilers is a major problem as power generators strive to improve the efficiency of plants. The coal type has a major influence on the slagging propensity in furnaces. The correlation between predicted results using some of the existing slagging indices and the actual observations made in most conventional boilers has been poor, especially when their use is extended to different coals. In this thesis, a numerical model to predict coal ash particle deposition rate in pulverized coal boilers has been developed. The overall sticking probability of the particle is determined by its viscosity and its tendency to rebound after impaction. The deposition model has been implemented in the Fluent 12.1 software, and the effects of swirling motion ash particle viscosity on deposition rates have been investigated. The predicted results are in good agreement with the reported experimental measurements on the Australian bituminous coals. Also, a novel numerical slagging index (NSI) which is based on ash fusibility, ash viscosity and the content of ash in the coals has been developed. The incoming ash shows significant influence on slag accumulation in boilers. The results of assessment of the slagging potential using the NSI on a wide range of coals and some coal blends correlate very well with the reported field performance of the coals. The NSI has been modified to predict the slagging potential of some coal and biomass blends with < 20% biomass ratio. The results of predictions using the modified index on coals blended with sewage sludge and saw-dust are in good agreement with the experimental data.

The following work details an investigation into improving efficiency in pulverised-fuel- fired power stations. The particular area of focus is the splitter box; this is located in the pneumatic conveying pipeline within the power station. The conveying pipelines take the pulverised fuel from the mill to the burner face, at some point the air/fuel mixture has to be split to feed the individual burners. It is at these points that the splitter boxes occur, dividing the pipe into multiple legs. It is common for some of these splits to produce poor fuel balance between legs, leading to excess air being required for their combustion at the burner wall. The increased supply of air increases the chance of the formation of NOx gases as well as reducing the overall efficiency of the plant. The poor fuel balance is caused by a particle rope, a dense area of particle stratification that creates an area of high fuel density that is not easily divided by the splitter boxes. The objective of this work is to develop devices to improve the fuel balance at splitter boxes. The work involves an investigation into existing devices and station geometries to see why existing devices have not become commonplace in coal-fired power stations. It also involves conceptual design of devices and then their testing, both computationally and experimentally. Finally, the devices are assessed for their suitability for full-scale power station implementation. This thesis used both experimental and computational techniques to develop devices to overcome the problems at splitter boxes and successfully produced several devices that could be developed and deployed in full scale testing.