Calcium chloride wastewater is more common in industrial production and cannot be discharged directly for treatment.
The production of polytetrafluoroethylene, hexafluoropropylene and other fluorine chemical series, photovoltaic electronic crystal silicon projects such as the production of propylene oxide, waste hydrochloric acid and wastewater are mainly calcium chloride, calcium chloride as an important chemical product, in the industry, food processing industry and pharmaceutical field has been widely used, wastewater through the front-end purification, evaporation crystallization can produce calcium chloride products, turning waste into treasure.
The concentration of common calcium chloride wastewater is generally 3% to 10%, and some of the wastewater contains traces of fluoride ions, organic matter, miscellaneous salts and other components, and the composition is relatively complex.
For the characteristics of wastewater, such as high organic content, electrochemical oxidation/Fenton oxidation can be considered to degrade most of the organic matter; neutralization reaction is used to adjust the pH of wastewater to neutral, and the clarified liquid after flocculation and precipitation enters the clear water tank, and the precipitate is pressed and filtered for treatment.
Calcium chloride wastewater into the presence of fluoride ions, the general content is very low, 10 ~ 20ppm, fluoride ions are very corrosive, the subsequent evaporation equipment, can be removed by special resin adsorption before the wastewater into the evaporation equipment.
After pretreatment, the calcium chloride wastewater can be concentrated at the front end by using the MVR plate rising film evaporation process due to the concentration of the feed, and after concentrating to 25% concentration, it is discharged from the system, MVR is the abbreviation of Mechanical Vapor Recompression (MVR), which is an energy-saving technology that reuses the energy of the secondary vapor it generates itself, thus reducing the need for external energy.
In the use of double-effect forced circulation evaporator will concentrate evaporation concentration to 45% concentration, at this time due to the same ion effect, other miscellaneous salts in the wastewater will precipitate out, after the insulation settlement kettle, calcium chloride clear liquid into the next process, insulation settlement kettle bottom miscellaneous salt centrifugal filtration, when solid waste disposal.
Now calcium chloride products are mainly CaCL2.2H2O, and anhydrous CaCl2, GBT 26520-2011 “Industrial Calcium Chloride” main indicators are as follows.
①For the production of calcium chloride dihydrate, a single-effect forced circulation evaporator is mainly used to raise the concentration of calcium chloride from 45% to about 75%, as the boiling point of calcium chloride solution is very high at this time, the heat source is generally 230°C heat-conducting oil as the heat source. 75% or so of the concentrated solution is discharged from the evaporator and sent to the cooling crystallization slicer for cooling and slicing to get flaky calcium chloride dihydrate solids, the discharge pipeline and the slicer feeding tank need to be Equipped with heat tracing device.
②Production of anhydrous calcium chloride, generally 45% concentration of raw materials transported to the spray dryer, hot air drying, and granulation molding, the bottom of the dryer discharge valve outlet calcium chloride moisture content can not reach the national standard requirements, the need for supporting the fluidized bed dryer to further dry, you can get qualified calcium chloride products.