On an international basis, coal is used extensively for power generation and this is likely to remain the case well into this century. Although many standard tests are currently used to assess and select coals for combustion purposes, these have proven to be unable to predict coal burnout behaviour. For a power station based on coal combustion, a clear knowledge and understanding of the coals offered in the market is essential to achieve optimum conversions and to meet environmental constraints. There is, therefore, a need to develop suitable and efficient methods and techniques to characterise coals so that the combustion plant performance can be predicted more effectively. In the present work, a series of experiments were conducted to characterise chars obtained from a Drop Tube Furnace (DTF) and a 1 MW combustion rig from which the effect of particle size distribution on coal reactions during devolatilisation and combustion of pulverised coal have been studied. The effect of temperature on coal pyrolysis in the DTF was also assessed. The coals used in this study were mainly from South America whose coals are widely traded internationally, and were characterised by standard tests and a novel automated image analysis technique called the Reactivity Assessment Program (RAP). The morphology of the chars were examined manually and using an automated image analysis technique and thermogravimetric analysis. The aim of this study was to provide a better understanding of the RAP and the automatic image analysis of chars, particularly related to South American coals. The results indicated that temperature significantly influences the coal behaviour during devolatilisation, and hence, the reactivity and morphology of the char generated. The structure and morphology of the char were found to play a significant role in burnout of the residual char, with a significant effect of coal type and particle size. Multiple linear regressions of char properties, such as intrinsic reactivity, morphology, and burnout, against particle size and maceral content of the feed coal were performed. The results showed that there was only a good correlation of high temperature volatiles with macerals. Subsequently when rank was included in the regressions, the correlation remarkably improved in all cases. However, when a novel approach which involved the correlations of char properties with bands of the grey scale histogram (RAP profile) of the coals was performed, much better correlations were achieved. The initial improvement is related, evidently, to the inclusion of the variation of vitrinite structure with rank. The grey scale histogram of coal takes this stage further by including the variation in reflectance for all the macerals. Therefore, the results indicate that the RAP analysis provides a simple and objective technique to predict the combustion behaviour of coals.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:514634 |
| Date | January 2001 |
| Creators | Barranco Melendez, Richelieu |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/10197/ |
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