Coal water slurry gasification wastewater salt separation and crystallization zero discharge treatment system and coal water slurry gasification wastewater salt separation and crystallization zero discharge treatment method

Abstract

The invention discloses a coal water slurry gasification wastewater salt separation and crystallization zero discharge treatment system and a coal water slurry gasification wastewater salt separationand crystallization zero discharge treatment method, wherein the system comprises a pretreatment system, a salt separation system, a mirabilite crystallization system and a salt crystallization system. The method comprises: S1, pretreatment, S2, salt separation, S3, output of sodium chloride, S4, output of sodium sulfate, and S5, treatment of mother liquor. According to the present invention, on the basis of meeting of the operation requirements of the system, the repeated arrangement of the chemical softening, the filtering and the membrane system in the treatment of the coal water slurry gasification wastewater by the traditional high salt content wastewater treatment system is simplified so as to reduce the investment and construction cost of the system and reduce the energy consumptionof the pretreatment system; the salt separation system is optimized, wherein the reverse osmosis production water is mixed with the first nano-filtration concentrated water according to a certain ratio, and the obtained mixture is subjected to second-stage nano-filtration, such that the operating pressure of the second-stage nano-filtration is reduced, the recovery rate of the second-stage nano-filtration is improved, and the service life of the equipment is prolonged; and the crystallization system is optimized, and the recovery rates and the purities of sodium chloride and sodium sulfate are improved.

Description

Technical field: [0001] The invention relates to the field of coal gasification, in particular to a zero-discharge treatment system and method for coal-water slurry gasification waste water, salt separation and crystallization. Background technique: [0002] Coal-water slurry gasification technology is a coal gasification technology that uses coal-water slurry as the raw material for coal gasification. Due to the high reaction temperature and pressure of coal-water slurry gasification technology, the effective components in the coal-water slurry can be recovered in the gasifier. Complete conversion is achieved, and the organic matter, pollutants and solid impurities carried in the coal-water slurry and produced during the gasification process enter into the coal-water slurry gasification wastewater, and the coal-water slurry gasification wastewater can be recycled after being reused. The highest recovery rate is 80%; while the other 20% coal-water slurry gasification wastewa...

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Problems solved by technology

[0003] At present, for this part of coal-water slurry gasification wastewater, the following methods are generally used for treatment: 1. Directly send to the sewage treatment plant for treatment. Large-scale wastewater has seriously affected the development of the coal chemical industry; 2. Direct evaporation and drying, after evaporation and drying of coal-water slurry gasification wastewater, miscellaneous salts are produced. Miscellaneous salts are not only complex in composition, but also easy to dissolve, and pollutants will easily leak when stacked for a long time accidents, seriously pollute the environment, and do not meet current environmental protection requirements; 3. Use a high-salt wastewater treatment system for coal-water slurry gasification wastewater treatment, such as figure 1 As shown, there are the following problems: 1) The wastewater from coal-water slurry gasification is sequentially subjected to reclaimed water reuse treatment, concentrated treatment and salt separation treatment. The treatment system is generally equipped with chemical softening, filtration, membrane system, and ion exchange softening. The construction of a salt separation treatment system based on the concentration treatment system also needs to be equipped with chemical softening, filtration, advanced oxidation, salt separation, and evaporation crystallization; it can be seen that using The high-salt wastewater treatment system needs to repeatedly set up chemical softening, filtration, and membrane systems to treat coal-water slurry gasification wastewater, which leads to high construction costs and high energy consumption of the existing high-salt wastewater treatment system; 2) the existing high The salt separation system of the saline wastewater treatment system performs primary nanofiltration on the concentrated wastewater, and then performs secondary nanofiltration on the concentrated water. The operating pressure of the secondary nanofiltration is relatively high, resulting in secondary nanofiltration recovery. The efficiency is reduced, and the service life of the equipment is short; the water produced by the secondary nanofiltration is treated with salt separation, the concentrated water of the secondary nanofiltration is subjected to advanced oxidation to remove organic matter, and then thenardite is separated, and the mother liquor of salt evaporation separation is recovered by thenardite to improve the recovery rate, but did not pay attention to the purity of by-product sodium sulfate crystalline salt, the recovery of salt in various evaporation and frozen mother liquors, resulting in low purity of by-product sodium sulfate crystalline salt, high TOC, high miscellaneous salt production, and the increase of miscellaneous salt production is inevitable It leads to high cost of miscellaneous salt treatment, which increases the burden on coal chemical enterprises

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