A method for removing impurities from desulfurized gypsum in a power plant

Abstract

The invention relates to a method for removing impurities from desulphurization gypsum of a power plant. The invention adopts a reversible conversion principle that dihydrate gypsum can be rapidly dissolved, re-crystallized and converted into alpha-hemihydrate gypsum under the conditions that temperature is higher than or equal to 120 DEG C, pressure is higher than or equal to 0.15MPa, a pH value is 2.5-7 and an additive exists, and the alpha-hemihydrate gypsum can be also rapidly converted into dihydrate gypsum when being cooled in a water environment. The method for removing the impurities from the desulphurization gypsum of the power plant comprises the following steps: sieving a raw material for filtering out large-particle impurities; preparing reaction slurry, and carrying out water type hot pressing reaction, so that dihydrate gypsum is rapidly converted into alpha-hemihydrate gypsum; standing, and cooling, wherein alpha-hemihydrate gypsum in the slurry is converted into relatively large dihydrate gypsum particles; removing impurities to obtain a relatively pure gypsum material; carrying out water filtration to further remove small impurity particles and harmful soluble salt in gypsum; and obtaining slurry and a wet body or drying to obtain powder according to follow-up needs. The method for removing the impurities from the desulphurization gypsum of the power plant can be taken as a gypsum raw material purification process in preparation of calcium sulphate whiskers by virtue of the desulphurization gypsum, and can also be taken as a method for producing high-whiteness gypsum. The method for removing the impurities from the desulphurization gypsum of the power plant is simple, efficient and easy for mass production.

Description

technical field [0001] The invention relates to a method for removing impurities from desulfurized gypsum in power plants by using hydrothermal pressure reaction technology based on the reversible transformation characteristics of gypsum crystal form. The technical field of resource utilization of gypsum. Background technique [0002] Since 2003, new coal-fired power plants approved by the National Development and Reform Commission must install flue gas desulfurization devices if the coal-fired sulfur content exceeds 0.7%. Calcium-based wet flue gas desulfurization is currently the most widely used coal-fired flue gas desulfurization technology in the world. With this technology, 1 ton of sulfur dioxide (SO2) can be fixed, and 2.7 tons of desulfurization gypsum (CaSO4·2H2O) can be produced at the same time. At present, about 50 million tons of desulfurized gypsum are produced by industrial by-products in my country every year. The calcium sulfate content of these by-product...

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Problems solved by technology

[0003] At present, there are relatively few patents in the field of desulfurization gypsum removal. US Patent USP5215672 proposes a multi-stage hydrocyclone separation process for desulfurization gypsum purification; US Patent USP5500197 proposes multi-stage separation and purification using different particle sizes in desulfurization gypsum. The actual effect of these two methods is not good, because in desulfurization gypsum, some impurities are coerced with gypsum particles and unreacted calcium carbonate particles, and it is almost impossible to separate them by pure physical means.

Among the domestic desulfurization gypsum impurity removal patents, the more representative CN103588237 mentions a method for removing impurities by utilizing the crystal form conversion characteristics of gypsum, but the raw material treatment steps in the preparation process are complicated and are carried out under normal pressure. The temperature does not exceed 100°C, the crystal transformation is slow, time-consuming and low efficiency

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