NUMERICAL MODELING OF HEAT TRANSFER PROCESSES IN A COAL-FIRED VORTEX FURNACE WITH BOTTOM-PORT SECONDARY BLOWING: ECOLOGICAL PERFORMANCE COMPARISON OF TWO TYPES OF COAL FUEL

Abstract

The work was devoted to numerical three-dimensional modeling of aerodynamics and pulverized-coal combustion processes in a novel vortex furnace of a boiler unit for thermal power stations. A prospective retrofitting design of this furnace, featuring additional tangential blowing at the bottom part of the vortex combustion chamber, was studied. Two types of Siberian coal at air excess coefficient 1.15 were used in the firing regimes: black coal (case K) and brown coal (case B). Numerical simulation of case K was performed at the Kuznetsk black coal feeding rate of 3.5 kg/s and the obtained aero-thermo-chemical structure in the novel vortex furnace was analyzed, its thermal-engineering parameters were calculated, including the nitrogen oxide (NOx) emission value of 851 mg/m³. These results were compared to the previously obtained numerical predictions for brown coal combustion (case B) at a feeding rate of 3.75 kg/s, where the NOx emission was 465 mg/m³. This comparison demonstrated larger levels of the temperature and nitric oxide (NO) concentration inside the combustion chamber in case K. Next, the contributions of the thermal mechanism of NO formation and the fuel-nitrogen mechanism were separately assessed in the NOx post-processing simulations, and these results obtained for cases K and B were compared. From this analysis it was concluded that, compared to black coal, the properties of brown coal (larger wet content and smaller amount of free nitrogen) help to diminish NO formation; therefore, the use of brown coal is preferable as a solid fuel choice in novel vortex furnaces.