Study on the mechanism of unsteady combustion related to volatile in a coal-fired traveling grate boiler

There are a variety of low-grade and hard-to-burn coals used in grate boilers in China. Almost all of them are manufactured with arches to promote the efficiency and their applicability to various coals. However, those boilers sometimes suffer from the unsteady combustion known as “puff”, which degrades energy efficiency, emits smoke pollution and even damages components. The mechanism responsible for its occurrence has been speculated to be related to the abnormal combustion of volatile released from coal, however, the details have not been clearly known up till now. In this paper, an experimental system is set up to investigate the unsteady combustion mechanism in an industrial traveling grate boiler. Natural gas is used to simulate the volatile from coal. Under the condition of two typical air distribution modes, dynamic pressure signals at various flow rates with fixed stoichiometric ratio are measured and influence factors on the unsteady combustion are studied. The detailed combustion characteristics are analyzed with large eddy simulation. The simulation is in reasonable agreement with the experiment and further discovers the mechanism of the volatile-related unsteady combustion. Moreover, the frequency analysis of the experimental data also confirms this mechanism.