Effects of Lignite Predrying Degree on the Combustion and NO Generation in a 600-MW Lignite-Fired Boiler

Previous studies have shown that predrying can improve lignite combustion performance and lignite-fired boiler efficiency. This paper numerically investigated the effect of the lignite predrying degree on the combustion and NOx generation characteristics in a 600-MW lignite-fired boiler. The simulation models were firstly validated by the design value and part of the in situ data of the boiler, and then, the effects of the lignite predrying degree on the velocity, volatile distribution, combustion, and NOx generation were conducted. The results show that the moisture content of lignite affects the devolatilization, ignition, combustion, and NOx generation processes because moisture evaporation changes the temperature distribution. In addition, the NO concentration in the burnout zone is higher than that in the main combustion zone, which is different from the distribution of NO in a bituminous-coal-fired boiler. When the moisture content of lignite decreases, the devolatilization and ignition rate increase, the combustion intensity and flue gas temperature increase, and the NO production and the heat transfer between the flue gas and the water-cooled wall increase as well.