Co-firing sludge is one of the important approaches to address the challenges of urban sludge accumulation. The field test of co-firing sludge dried by flue gas was conducted in a 350 MW supercritical coal-fired power unit to investigate the effects of blending amount and unit load on system operation and energy consumption. Wet sludge was dried using extracted boiler tail flue gas, with the dried sludge subsequently carried into the furnace for co-combustion. The results show that a positive correlation exists between the wet sludge amount and the temperature/flow rate of drying flue gas. Drying 11 t/h wet sludge required 71 t/h flue gas at 597 ℃. As the sludge blending ratio rose, the boiler thermal efficiency decreased, while the auxiliary power consumption ratio increased. The rise in sensible heat loss in exhaust gas mainly led to the decline in boiler thermal efficiency, and the rises in both unburned carbon heat loss in residue and sensible heat loss in residue were secondary factors. The rise in auxiliary power consumption ratio was primarily attributed to the high power consumption of the sludge drying system, with sludge co-combustion system dominating the rise in auxiliary power consumption ratio. The rise in net coal consumption rate was caused by the decline in boiler thermal efficiency and the rise in auxiliary power consumption ratio, and the rise in auxiliary power consumption ratio contributed more significantly. At 262 MW and with a sludge blending mass ratio of 8.76% (sludge moisture fraction: 83%), the boiler thermal efficiency decreased by 0.260%, the auxiliary power consumption ratio increased by 0.466%, and the net coal consumption rate increased by 2.38 g/(kW·h). The study provides a reference foundation for the energy consumption evaluation and optimization of co-firing sludge dried by flue gas in a coal-fired power unit.

coal-fired power unit  /  sludge dried by flue gas  /  boiler efficiency  /  auxiliary power consumption ratio  /  fuel/coal consumption rate