Abstract: Abstract: Emission of fine particles can be controlled effectively in the wet flue gas desufurization (WFGD) system by the combining vapor heterogeneous condensation technology. Fine particles removal efficiency is influenced directly by the supersaturation degree of desulfurated flue gas with water vapor added. The supersaturation degree of desulfurated flue gas depends on the temperature and humidity of desulfurated flue gas and the amount of water vapor added. Hence the research of variation characteristics of desulfurated flue gas temperature and humidity would provide a basis for fine particles removal in WFGD system combined with vapor heterogeneous condensation. The results are significant to the optimization of WFGD operating conditions, the estimation of the amount of water vapor added and the fine particle removal with high efficiency and low energy. Based on the limestone-based desulfuration process, the influences of the temperature and humidity of inlet flue gas, superficial gas velocity, liquid-to-gas ratio, desulfurization solution temperature etc. on the temperature and humidity (absolute humidity and relative humidity) of desulfurated flue gas were investigated in this paper. The results showed that the relative humidity and absolute humidity of desulfurated flue gas would first decrease sharply from 88%, 82.2 g/kg to 52%, 57.3 g/kg respectively, and then become flat when the superficial gas velocity increased from 2.5 to 2.9 m/s. An increase of liquid-to-gas ratio from 5 to 20 L/m3 was beneficial to enhance the absolute humidity and relative humidity of desulfurated flue gas. They increased from 39%, 46.4 g/kg to 91%, 84.3 g/kg, respectively. The increase amplitude of relative humidity was much higher than that of absolute humidity. With the increasing of the temperature of desulfuration solution, the temperature, absolute humidity and relative humidity of desulfurated flue gas enhanced significantly. If the desulfurization liquid temperature rose from 25 to 60 ℃, the relative humidity, absolute humidity and temperature of desulfurated flue gas could enhance from 54%, 25.9 g/kg and 42 ℃ to 85%, 98.5 g/kg and 56 ℃, respectively. However, the flue gas relative humidity became flat while the desulfurization solution temperature increased to 40 ℃. If the temperature of desulfurization solution was kept constant, the absolute humidity and temperature of desulfurated flue gas increased evidently early and became flat afterward with an increase of inlet flue gas temperature, while the relative humidity decreased slightly. When a spray tower was used as desulfurization tower, the higher relative humidity of desulfurated flue gas could be obtained under the following conditions: superficial gas velocity smaller than 2.5 m/s, liquid-to-gas ratio higher than 15 L/m3, desulfurization liquid temperature of about 50 ℃, relative humidity of inlet flue gas of desulfurization tower larger than 15%, and temperature of inlet flue gas of desulfurization tower lower than 110 ℃. Moreover, the types of desulfurization tower also could affect the temperature and humidity of desulfurated flue gas. When the liquid-to gas ratio was 5 L/m3, the relative humidities of desulfurated flue gas at the outlet of turbulent ball tower, rotating-stream-tray tower and spray tower were 90%, 91% and 44%, respectively.