Basic experimental on solidification for high salt desulfurization wastewater in coal-fired power plant

Under the background of zero liquid discharge of flue gas desulfurization (FGD) wastewater, the conventional evaporation and crystallization process can't effectively avoid the secondary pollution of FGD wastewater. Thus, a technical route of concentrating FGD wastewater using flue gas wasteheat and solidification with cement is proposed. In the concentration tower, the FGD wastewater is evaporated and concentrated by using part of the flue gas after the electric precipitator, and the concentrated FGD wastewater can be mixed with cement, fly ash and other materials to obtain solidified blocks, thereby realizing the solidification of the pollutants. Simulated high-salt water is mixed with cement, fly ash and river sand to obtain measurement blocks in the experiment. After curing to a specific time, the compressive strength and the Cl- binding capacity of the blocks is tested. The impact of different component materials on the compressive strength and the Cl- binding capacity of the blocks is investigated by using the method of controlling univariate, and the powder from measurement blocks is characterized by XRD. The results show that the compressive strength of measurement blocks reaches the highest value when the cement ratio is 1.08, and increases when the fly ash ratio is greater than 0.25. The higher the percentage of high-salt brine, the lower the compressive strength, and the percentage of river sand in block has little effect on the compressive strength of blocks. After 28 days of curing, the measurement blocks prepared in the experiment has a compressive strength value of more than 30 MPa, which can meet the minimum compressive strength requirement of the curb in the standard of Concrete Curb. With the increase of the pecentage of cement, the Cl- binding capacity of the blocks increases by 21.7%, and the increase trend is limited by the amount of water required for cement hydration, so it is gradually slowed down. Due to the lower amount of Friedel's salt which is produced by the reaction of the pruduct of fly ash in the process of cement hydration with Cl-, the Cl- binding capacity of the blocks only increases by 4.9% with the increase of the pencentage of fly ash. The results of XRD verify the existence of Friedel's salt during the solidification. © 2019, Editorial Office of Journal of China Coal Society. All right reserved.