Numerical simulation of combustion process for a slag tapping boiler

In order to investigate the combustion process and NOx formation properties in a coal water slurry fired slag tapping boiler, a three dimensional computational fluid dynamics (CFD) simulation work was conducted. Standard k-ε turbulence model and non-premixed combustion model was used here. Specially, for the treatment of particle during the slag tapping combustion process, particle trapping method was used for the surface boundary condition. The flow field, temperature and oxygen distribution as well as NOx in the furnace were analyzed and validated with real case experimental data. Results show that the combustion process in the furnace are all complete at the three different air feeding modes. Compared to typical air feeding conditions, temperature distributes in the furnace is more uniform at staged air method. The swirl secondary air on the top together with tangential secondary air enhances the airflow distribution in the furnace. This also enhances the combustion process and maintains the whole furnace running at a high temperature level, which is need by the downstream petroleum cracking process. The exiting of downstream secondary air enhances the burn out of the coal particles and inhibits NOx emission to 684 mg/m3 at staged combustion mode. Therefore, the coal water slurry fired slag tapping boiler can be running well at staged combustion mode with uniform temperature distribution and low NOx emission.