Softening of wastewater from wet flue gas desulfurization process based on internal airlift loop reactor (IALR)

The slurry discharge water from the flue gas desulfurization process in coal-fired power plant is rich in high salinity and chloride. The hardness may easily lead to scaling during the wastewater treatment. The internal airlift loop reactor based NaOH and CO 2 two-step approach is employed to investigate the softening of flue gas desulfurization wastewater treatment. NaOH is used to precipitate the dissolved magnesium in the first step. CO 2 is used to precipitate the dissolved calcium in the second step. The magnesium removal rate of 99% is obtained at the molar concentration ratio of NaOH and magnesium of 2.2 and aeration rate of 1 L min –1 . The optimized calcium removal condition is CO 2 concentration of 15% by volume, temperature of 30°C, initial pH of 12.8 and aeration gas rate of 7 L min –1 . The residual magnesium and calcium of 4.6 and 43.8 mg L –1 were detected in softening experiment with the coal-fired power plant flue gas desulfurization wastewater. The resultant CaCO 3 is the crystal calcite, which is a pure and regular flaky block and can be used as desulfurizer for wet flue gas desulfurization. This work provides the potential pretreatment solution for large scale flue gas desulfurization wastewater treatment.