Abstract: Taking two Zhejiang power plants as the research objects, the difficulties of zero discharge control technology for desulphurization wastewater from bypass flue gas drying tower are analyzed. In order to keep the quality of fly ash unchanged, a multi-parameter control model is established to determine the minimum flue gas temperature and the maximum desulphurization wastewater treatment capacity under the consideration of flue gas acid dew point. At the same time, the accurate control technology based on energy balance and the soft sensing model based on key parameters are both implemented to backup each other, such that the goal of high efficiency and low energy consumption drying of desulphurization wastewater is achieved. The calculation of desulphurization water quality control limit of Taizhou Second Power Plant shows that fly ash can be recycled as ordinary concrete additive. As for the drying tower of Changxing Power Plant, with the flue gas baffle door fully open, when the inlet temperature is 35℃ and the mass flow rate of desulphurization wastewater reaches 4 200 kg/h, the outlet temperature still remains at 117℃, but once the inlet temperature of flue gas drops to 280℃ and the outlet temperature climbs above 110℃, the output of the system then becomes 1 750 kg/h, which is basically consistent with the theoretical expected value based on energy balance algorithm.

Key words: coal-fired power plant, desulfurization wastewater, zero emission, bypass flue gas drying tower, multi-parameter control model, deep peaking