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

Abstract

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. NO_x 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 NO_x 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 NO_x 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 NO_x mole fraction at the furnace outlet decreases from 4.1696 × 10⁻⁵ to 3.9862 × 10⁻⁵.