Numerical simulation of a decoupling and Re-burning combinative Low-NOx coal grate boiler

A two-dimensional computational fluid dynamic model was developed to simulate the combustion process and nitrogen oxides formation of a 1.5 MW decoupling and re-burning combinative low-nitrogen oxides coal grate boiler to facilitate the design. FLUENT coal calculator was used for the combustion of over bed coal volatiles, along with the post-process nitrogen oxides formation. By comparing the combustion and pollutants emission of several designs, the nitrogen oxides emission and stable combustion effects of the new grate boiler were investigated. The effects of different boiler length and different pyrolysis gas injection sizes were analyzed to optimize the boiler structure. The computational results were found to match well with experimental data. Results showed that the decoupling and re-burning combinative technique gave considerable improvements in combustion efficiency and nitrogen oxides reduction and has excellent potential for future application. The optimization work revealed that a furnace arch length of 1.5 m and injecting the pyrolysis gas through the small hole on front wall of the furnace may be considered as a comparatively well-organized mode. Meanwhile, the results showed that a variety of factors, such as the disturbance intensity, air/coal ratio in the combustion zone, mixing zone size of the pyrolysis gas and main flow, etc., can significantly affect combustion efficiency and nitrogen oxides emissions.