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Coal Combustion Modelling

AUTHOR: Stephen Niksa
DATE: December 1996

This Perspectives report surveys the literature on evaluation of computer simulations of full-scale, coal-fired utility surfaces against field test data. Introductory sections reiterate what is known about the basic principles of operation of large coal flames, and survey how these ideas are translated into mathematical submodels. Later sections classify and develop applications as macroscopic furnace operating characteristics, process control, coal quality impacts, and design.

Applications based mostly on particle trajectories, such as whether wall impingements are likely, are especially secure. Simulated unburned carbon levels in ash also can be remarkably accurate, provided that the modelling programme is supported by a database on furnace performance and test burns. But for 3-D simulations of irregular full-scale furnace geometrics, details in simulated flow patterns can be regarded as grid artifacts unless the simulations are shown to be grid independent, which is rarely done. The three most important applications involving the chemistry are coal quality impacts and CO and NO emissions. There are no published simulations of CO concentration fields for full-scale furnaces exhibit major discrepancies with the accompanying measurements. Simulators have been tuned-in to measured exhaust NOx concentrations, but novel burner idea with unusual internal flow passages have confounded simulators with the standard NO production mechanism.

Recommendations for future applications focus on the volatiles combustion submodel and tradeoffs between more realistic chemical mechanisms and uncertain turbulence-chemistry interactions.