Effect of Bituminous Coal Properties on Heat Transfer Characteristic in the Boiler Furnaces

Over the past years experience has been gained in employing changing types of imported coal. Apart from the proximate analysis this led to development of evaluation criteria regarding the operation of coals. These are criteria numbers obtained from operational experience and criteria numbers used for the characterization of specific operational properties on the basis of special laboratory analyses. The study evaluates the effect of the characteristics of pulverized coal on the furnace fouling and radiation heat transfer. The aim of the study was to access whether fouling and radiation heat transfer could be predicted from coal characteristics. The paper presents the experimental results on the fouling propensity of fifteen coals tested in a 575 MW combustion engineering tangential firing boiler. The results showed that no coals produced a strong molten deposit. In order to rank the fouling propensity and radiation heat transfer properties numerically, we measured the profile of incident heat fluxes, defined furnace exit flue gas temperature and absorbed heat fluxes. The basic molar ratio correlates the fouling propensity. Besides that increasing of SiO₂ and Al₂O₃ content in the ash strongly reduces water wall absorptivity factor. The present work is also concerned with the effect of different bituminous coal on their flame emissivity. Using the radiation properties of flue gases derived from the full scale experiments, we run computational fluid dynamics (CFD) on the combustion process. The known fouling and radiation heat transfer properties enable the prediction of the effect of coal quality on the performance of a specific boiler.