Coal pyrolysis is the initial coal reaction step during combustion or gasification processes. The secondary pyrolysis of volatile compounds, including coal tar and light gases, accounts for a great portion of soot formation and the subsequent heat release and pollutant formation. While coal primary pyrolysis has been extensively studied over the last few decades and several network models have successfully described this process, coal secondary pyrolysis is still not well understood and as such, it is generally oversimplified. For this reason. The Babcock and Wilcox Company has been investigating coal secondary pyrolysis in order to develop a comprehensive mechanism for inclusion in predictive computational fluid dynamics and coal combustion models. An entrained-flow reactor, a flat flame burner, and a state-of-the-art laser diagnostic system have been utilized to study the formation and evolution mechanisms of tar, soot, and light gases. This paper discusses the experimental results, reaction mechanisms, and their dependence on the coal structure.
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