Abstract:of 660 MW coal-fired unit was upgraded to increase its capacity and efficiency. Applying mixed com⁃bustion of economical coals, the economic efficiency of the desulfurization system was analyzed bychanging the load and sulfur content of coal. The calculation models were established based on desulfu⁃rization performance, desulfurization cost per unit power supply, and hourly average operation cost. Theoperation cost and potential of the desulfurization system were analyzed. The results showed that, whenthe unit operated at 100% load and met the ultra-low emission requirements, the maximum SO2contentof raw flue gas that the desulfurization system could withstand was 2 320 mg/Nm3, which equaled to acoal sulfur content of 1.1%. When the sulfur content of coal in furnace was greater than 0.85%, thehourly average desulfurization cost increased rapidly. When the sulfur content of coal in furnace in⁃creased to more than 1.1%, all equipments of the system operated at full capacity, with lack of redun⁃dancy and poor reliability. The desulfurization system had a good performance in economy andreliability when the the sulfur content of coal in furnace was 0.66%~0.85%. Close-