Power plants utilizing substandard coal for electricity generation often face reduced denitrification efficiency due to high fly ash concentrations in the flue gas, which complicates achieving ultra-low emissions. The flue gas duct from the economizer outlet to the riser duct entrance in the W-shaped flame boiler at Guizhou Chayuan Power Plant was investigated. Numerical simulations were conducted to analyze flue gas flow and fly ash particle trajectories. The results show that the economizer ash hopper is minimally effective, with a collection rate of only 9.99%. Simulation results reveale fly ash deposition on the wall at the SCR riser flue bend at 1.12 kg/s, representing 11.33% of total fly ash. Based on these findings, two design schemes for positioning a denitrification ash hopper below the riser flue are proposed to enhance fly ash collection efficiency. Optimal results are obtained with a 45° angle between the inclined surface and horizontal wall, increasing fly ash collection by 8.38% with a 2.25 Pa pressure drop increase.