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Title：How does MVR extract salt by quality? MVR salt extraction process
At present, the amount of industrial wastewater treatment is large, and the composition of wastewater is complex and changeable, and the treatment is difficult, especially the treatment of multi-component saline wastewater is difficult. Let's talk with Cheng Xiaobian about the MVR mass extraction salt evaporation crystallization system.
1、 Evaporative crystallization process of salt extraction by mass
The mass extraction evaporation crystallization process mainly utilizes the difference between the solubility of sodium sulfate and sodium chloride and the temperature dependence. At 50~120 ℃, the solubility of sodium sulfate decreases with the increase of temperature, while the solubility of sodium chloride increases with the increase of temperature.
The solubility of sodium ion, chloride ion and sulfate ion system at different temperatures in three-phase co-saturation, and the crystallization temperature should be designed to ensure that the solubility of sodium sulfate and sodium chloride has a certain difference, and the temperature should not be too low.
In the actual industrial production process, the evaporation of sodium sulfate and sodium chloride solution is large, and the crystallization end point is generally required to be lower than the saturation concentration.
2、 Common salt extraction technology based on quality
1. Multi-effect evaporation system occupies an important position and has certain advantages in performance analysis and optimization.
However, the equipment of multi-effect evaporation system is huge, the consumption of raw steam is large, and the large amount of latent heat in the final effect secondary steam is also difficult to use, resulting in waste.
2. MVR evaporation technology and mechanical steam recompression technology reduce the demand for external energy by reusing the latent heat of secondary steam.
3、 MVR mass extraction salt evaporation crystallization system
Working process of MVR evaporation and salt separation evaporation and crystallization system:
For the feed liquid, the high-temperature steam condensate from the heating chamber of the first-effect falling-film evaporator and the second-effect forced circulation evaporator will first exchange heat with the first-effect falling-film evaporator through the first-stage preheater, and then enter the first-effect falling-film evaporator for heat exchange and evaporation after reaching the set evaporation temperature. After the sodium sulfate component in the feed liquid reaches saturation, it will enter the second-effect forced circulation evaporator for supersaturation evaporation (at this time, the sodium chloride component in the feed liquid will be concentrated to close to saturation), The generated crystal slurry is sent to the primary crystallization separator, and the sodium sulfate component is sent to the sodium sulfate crystal storage tank after separation.
The concentrated solution produced after separating sodium sulfate will exchange heat with the condensed water from the preheater through the secondary preheater. After reaching the set evaporation temperature, it will enter the three-effect forced circulation evaporator for supersaturation evaporation. The generated crystal slurry will be sent to the secondary crystallization separator. The sodium chloride component will be sent to the sodium chloride crystal storage tank after separation. Some concentrated solution will return to the forced circulation evaporator through the circulation pump and continue to evaporate to the crystal discharge volume, Discharge the remaining concentrated liquid through the unloading valve.
The solubility of sodium sulfate and sodium chloride is determined at a certain evaporation temperature, so the saturation concentration under the corresponding state can be determined, and the saturation or supersaturation state of sodium sulfate and sodium chloride can be controlled by the ion concentration meter.
