CPFD numerical study on tri-combustion characteristics of coal, biomass and oil sludge in a circulating fluidized bed boiler

To study the tri-combustion characteristics of coal, biomass, and oil sludge, the computational particle fluid dynamics (CPFD) method is employed to simulate the flow, heat transfer, and combustion processes in a 130 t h−1 circulating fluidized bed (CFB) boiler. The effects of blending ratio, secondary air inlet angle, and excess air coefficient are evaluated in detail. The results show that the mole fraction of SO2 in the furnace is slightly lower than that in the cyclone separator. NOx has high mole fraction near the fuel inlet. As the biomass blending ratio rises from 30 % to 50 %, the O2 mole fraction at the furnace outlet increases from 0.0601 to 0.0629, while CO2 exhibits the opposite tendency. The highest and lowest NOx mole fractions at the furnace outlet are 4.1648 × 10−5 and 3.9862 × 10−5, respectively. As the blending ratio of oil sludge rises from 10 % to 20 %, the mole fraction of SO2 at the furnace outlet increases from 3.3041 × 10−4 to 4.8952 × 10−4. The mole fraction of NOx in the furnace shows a positive correlation with the excess air coefficient, while SO2 is on the contrary. As the jet angle increases from 15° to 30°, the NOx mole fraction at the furnace outlet decreases from 4.1696 × 10−5 to 3.9862 × 10−5.