Zero discharge system for high-efficiency low-cost desulfurization wastewater treatment of coal-fired power plant

Abstract

The invention relates to the field of wastewater treatment, in particular to a zero discharge system for high-efficiency low-cost desulfurization wastewater treatment of a coal-fired power plant. Thezero discharge system comprises a pretreatment unit, a concentration reduction unit and a tail end curing unit, the pretreatment unit is used for removing suspended matters, fluoride, sulfide and heavy metal ions in the wastewater through flocculation reaction, reducing chemical oxygen consumption and ammonia nitrogen and effectively adjusting the pH value; pretreated water of the pretreatment unit is treated by the concentration reduction unit in a direct contact type thermal concentration mode, obtained wet flue gas enters a desulfurizing tower to be treated, obtained precipitated mud entersa tail end solidification unit, and obtained mud supernatant strong brine circularly enters the concentration reduction unit to be treated; after mixing of a tail end curing unit precipitated slurrywith fly ash, quick lime, ferrous sulfate and an inorganic polymerizing agent, a low-grade building material if formed. Flue gas waste heat is used for concentrating desulfurization wastewater, the inlet flue gas temperature of the desulfurization tower is reduced, and the evaporation water consumption of the desulfurization tower is reduced; the wastewater recovery rate is high, and the water-saving purpose is achieved.

Description

technical field [0001] The invention relates to the field of waste water treatment, in particular to a zero-emission system for high-efficiency and low-cost desulfurization waste water treatment in coal-fired power plants. Background technique [0002] Coal-fired power plants that use coal as fuel will produce harmful substances such as sulfur dioxide during the combustion process. The limestone-gypsum wet flue gas desulfurization process is widely used in coal-fired power plants to remove sulfur dioxide and other pollutants in the flue gas. The limestone-gypsum wet flue gas desulfurization plant produces a large amount of desulfurization wastewater during operation, such as: 2×300MW units, the desulfurization wastewater discharge is generally 2.5-14m 3 / h, average 7.9m 3 / h; 2×600MW units, the discharge of desulfurization wastewater is generally 6-25m 3 / h, average 16m 3 / h; 2×1000MW units, the discharge of desulfurization wastewater is generally 25-30m 3 / h, average 27...

AI Technical Summary

Problems solved by technology

[0005] 2) In terms of softening process, the mainstream softening technology of desulfurization wastewater is chemical softening process. Since desulfurization wastewater contains high concentrations [several thousand ppm or even as high as 20000 ppm] of scale-causing ions such as calcium, magnesium, strontium and barium, chemical softening process needs to be added A large number of chemical softening agents, the cost of chemicals is very high, accounting for the vast majority of the cost of chemicals in the zero-emission system; construction of large-scale chemical softening process equipment covers a large area and requires high investment; and produces a large amount of chemical softening sludge, resulting in high disposal costs; Water TDS does not drop but rises, increasing the burden of subsequent concentration reduction and terminal curing, increasing the investment and operating costs of concentration reduction and terminal curing

The evaporation crystallization process requires the establishment of a large-scale evaporation crystallization system, which consumes a lot of steam and electricity, occupies a large area of ​​land and buildings, and has high construction and operation and maintenance costs; the flue spray evaporation technology makes the waste water flow in the flue (bypass) Atomized injection, evaporation, impurities in the wastewater enter the dust removal equipment with the flue gas in the form of solid matter and fly ash, the main problems are:

[0009] a. Chlorides and heavy metals are enriched in fly ash; they greatly affect the reuse of fly ash and the safety of users

[0010] b. After the desulfurization wastewater evaporates, the highly corrosive chlorides cannot be completely collected by the electrostatic precipitator, causing them to accumulate on the desulfurization tower and subsequent equipment, causing severe corrosion and scaling, which significantly increases the frequency of equipment maintenance and maintenance costs; reduces The dust removal efficiency even affects the normal operation of the electrostatic precipitator;

[0011] d. This process mainly relies on the electrostatic precipitator to remove the evaporative crystallization products. The substances that the electrostatic precipitator cannot remove will return to the desulfurization tower with the flue gas, and will be enriched in a continuous cycle, increasing the load of the desulfurization tower, and causing PM2.5 and mercury, etc. Emissions are easy to exceed the standard

[0012] c. The spray evaporation technology is restricted by the flue gas temperature and flue gas dew point temperature, and the amount of desulfurization wastewater that can be evaporated is limited; if the high-temperature flue gas is evaporated before the air preheater, the efficiency of the unit will decrease and the coal consumption will increase.

[0013] e. Rapid failure of the atomizing nozzle makes it difficult to maintain the designed atomization level for a long time

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