Treatment of Desulfurization Wastewater by Ion Exchange Method
Macroporous mercapto (-SH) ion exchange resins are used to adsorb mercury ions for the purpose of removing mercury ions from water. The adsorption method is based on the adsorption principle of activated carbon: activated carbon has an extremely large surface area, and oxygen-containing functional groups (-COOH, -OH, -CO) are formed during the activation process, endowing activated carbon with the properties of chemisorption, catalytic oxidation and reduction, which enables effective removal of heavy metals.
Treatment of Desulfurization Wastewater by Electrocoagulation Method
Electrocoagulation technology is also applied to the wastewater treatment of wet desulfurization. Based on electrochemical principles, electrocoagulation dissolves soluble electrodes under the action of electric current, converting them into charged ions and releasing electrons, thus generating flocculating compounds. In addition, the released electrons reduce positively charged pollutants, achieving the goal of removing pollutants from the liquid.
Electrocoagulation can effectively treat heavy metals and has the advantages of compact equipment layout, low cost of treatment chemicals and good treatment effect. However, it features a relatively complex process: conventional electrocoagulation cannot remove chloride ions, while high-frequency electrocoagulation has drawbacks such as high energy consumption and limited electrode service life. At present, electrocoagulation technology has been applied in oil-containing wastewater and chemical wastewater with high heavy metal content, but it has not been popularized in desulfurization wastewater treatment.
Evaporative Treatment of Desulfurization Wastewater
The wastewater is pretreated by traditional chemical dosing. The pretreated wastewater is heated by a preheater and then fed into the evaporation system, which is mainly divided into four parts: the heat input section, heat recovery section, crystallization and transportation section, and auxiliary system section.
Desulfurization wastewater is heated and concentrated in four-stage evaporation chambers and then sent to a salt slurry tank, and pumped into a salt hydrocyclone by two salt slurry pumps. The hydrocyclone separates large-grain salt crystals by cyclonic action, which then fall into the centrifuge below. The salt crystals separated by the centrifuge are conveyed to a drying bed by a screw conveyor for heating to achieve complete drying of the salt crystals. The slurry separated by the hydrocyclone and centrifuge is returned to the heating system for re-heating, evaporation and concentration. The dried salt crystals are transported out of the plant by truck.
This method combines the advantages of both the concentration crystallization method and evaporation concentration method, boasting a high system recovery rate: wastewater is basically treated and recycled with no waste liquid discharge except for partial drying loss; the system only requires chemical cleaning once or twice a year, resulting in low management and maintenance workload; it reduces the possibility of scaling on heat transfer surfaces and the dosage of inhibitors; the quality of water recovered by evaporation is high. Nevertheless, it has disadvantages such as complex equipment layout, high control requirements and high energy consumption, and is currently still in the experimental research and development stage.
These new technologies can effectively remove heavy metals and even chloride ions from desulfurization wastewater. However, they have not been applied and popularized in domestic power plants due to restrictions from various factors such as technology, conditions, the environment and investment. At present, only a small number of overseas projects have been put into use, and some key control parameters and processes are still in the research and development stage.
