Power plant desulfurization wastewater zero-discharge treatment process based on electrodialysis technology and system thereof

Abstract

The invention relates to a power plant desulfurization wastewater zero-discharge treatment process based on an electrodialysis technology and a system thereof, and belongs to the field of water treatment. The treatment process comprises the following steps: raw desulfurization wastewater enters a triple tank for process treatment; effluent of the triple tank enters a clarification tank; settled sludge is generated in the process treatment of the triple tank and the clarification tank; the filtered effluent enters a nanofiltration membrane system for primary salt separation of monovalent ions and divalent ions; fresh water in the nanofiltration membrane fresh water tank enters a monovalent cation selective electrodialysis system; concentration is carried out by an SWRO system to obtain reverse osmosis concentrated water with relatively high concentration; the concentrated solution is mainly high-concentration sodium chloride saline water; in a nanofiltration membrane concentrated water tank, nanofiltration concentrated water and reverse osmosis concentrated water are mixed to form magnesium sulfate concentrated water, the magnesium sulfate concentrated water enters a freezing crystallization magnesium sulfate system to generate magnesium sulfate salt for sale, and generated freezing crystallization mother liquor enters a mother liquor two-stage nanofiltration membrane to obtain mother liquor fresh water and mother liquor concentrated water; and mother liquor fresh water is mainly a mixed solution of sodium chloride and magnesium salt.

Description

technical field [0001] The invention relates to a zero-discharge treatment process and system for power plant desulfurization wastewater based on electrodialysis technology, belonging to the field of water treatment. Background technique [0002] 1. Brief introduction to the development of this technical field: [0003] Desulfurization wastewater is produced by coal-fired power plants containing a large amount of SO 2 The flue gas is often treated with wet desulfurization to obtain industrial wastewater. In order to maintain the balance of substances in the slurry circulation system of the desulfurization unit, prevent the soluble part of the flue gas, that is, the chlorine concentration from exceeding the specified value, and ensure the quality of the gypsum, a certain amount of desulfurization wastewater must be discharged from the system. The desulfurization wastewater mainly comes from the gypsum dehydration and cleaning system. The impurities contained in wastewater m...

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Problems solved by technology

[0005] (1) Its high concentration of suspended solids seriously affects the turbidity of water, and it is easy to cause scaling in equipment and pipelines, which affects the operation of desulfurization devices;

[0006] (2) Desulfurization wastewater is weakly acidic, and heavy metal pollutants have good solubility in it. Although their content is small, direct discharge has a certain poisonous effect on aquatic organisms; the concentration of chloride ions in wastewater is high, which will cause Corrosion of equipment and pipelines will seriously affect the operation and service life of the absorption tower when the concentration reaches a certain level, and will also reduce the desulfurization efficiency and affect the quality of gypsum;

[0007] (3) The effect of fluoride ions is similar to that of chloride ions, but because fluorine can form calcium fluoride with calcium and precipitate, the content in desulfurization wastewater is relatively small. In addition to affecting the quality of gypsum, it also affects the tower body. The corrosion of pipelines is much smaller than that of chloride ions, but fluoride ions and Al in limestone slurry tend to produce a colloidal floc, which forms a coating to cover the surface of limestone particles, hindering the dissolution of limestone. Affect the desulfurization efficiency;

[0008] (4) Direct discharge of high-concentration sulfate in desulfurization wastewater into the environmental water body will cause the loss of trace metal elements necessary for aquatic plants and change the original ecological function of the water body;

[0009] (5) The discharge of a large amount of toxic substances in desulfurization wastewater will pollute the soil and water sources, affect the health of humans and animals, and cause chronic poisoning if accumulated for a long time

[0034] (1) Multi-effect evaporation crystallization process: Although the technology is relatively mature, the extremely high energy consumption of this treatment process limits its promotion in the field of zero discharge of desulfurization wastewater

[0035] (2) MVR evaporation crystallization process and exhaust to high temperature flue evaporation process: most of the crystallized salts obtained are NaCl, Na 2 SO 4 Miscellaneous salts composed of different components, some are even classified as hazardous waste, and the disposal cost is high

[0036] (3) Membrane distillation process: Membrane distillation has been studied more and more in recent years because of its low operating temperature, small equipment required, and low external heat loss, but it basically stays in the laboratory stage because of its difficult amplification and latent heat. The difficulty of recovery and other problems hinder the industrial application and promotion of membrane distillation

[0037] 3. For a desulfurization wastewater treatment process and treatment system in the patent No. CN111170538A: although desulfurization wastewater can be effectively treated to achieve zero discharge, silicon substances always exist in the entire process chain in its process flow , it is easy to cause silicon enrichment problem, which will cause irreversible impact on membrane processing equipment

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