Lithium iron phosphate in new energy batteries is neutralized by ammonia method to produce ammonium chloride wastewater. A certain amount of ammonium chloride wastewater is produced in the chemical fertilizer industry and rare earth production. Due to the presence of ammonia nitrogen and chloride ions in ammonium chloride wastewater, if ammonium chloride wastewater Direct discharge will cause damage to the water body. Therefore, ammonium chloride wastewater generally needs to be desalted before entering the back-end treatment process, and the by-product ammonium chloride can be used as agricultural fertilizer.
Ammonium chloride physical properties
Boiling point temperature rise of ammonium chloride:
Solubility of ammonium chloride:
Commonly used evaporation crystallization process of ammonium chloride are multi-effect evaporation, MVR evaporation
MVR evaporation equipment material selection
According to the corrosiveness of the ammonium chloride liquid solution, the part in contact with the material can be made of TA2 material, the part in contact with the secondary steam can be made of TA2/2205 material, and the part in contact with the condensed water can be made of 316L.
Technical principle
The realization process of ammonium chloride MVR evaporator is: ammonium chloride MVR evaporator concentration → ammonium chloride solution continuous crystallizer → crystallization and filtration → mother liquor return to MVR evaporator
By controlling the concentration of ammonium chloride solution in the MVR evaporator and controlling the highest boiling point of ammonium chloride solution to rise <12℃, a more satisfactory energy-saving effect can be achieved.
Because the mother liquor returns to the evaporator after the ammonium chloride solution is cooled and crystallized, it needs to consume some extra steam, and the steam consumption is proportional to the ammonium chloride content.
Ammonium chloride MVR evaporator adopts multi-stage evaporation process with a common single compressor. The concentration of ammonium chloride increases step by step, and the heat exchange temperature difference of the MVR evaporator gradually decreases. The maximum evaporation intensity is obtained at the stage, and the mother liquor after ammonium chloride cooling and crystallization is returned to the last stage of the ammonium chloride MVR evaporator, which does not affect the concentration of the front-end solution.
Ammonium chloride cooling crystallizer adopts cooling OSLO crystallizer, through the column tube heat exchanger to remove the heat of the high temperature and high concentration solution coming from the MVR evaporator, the temperature of ammonium chloride solution is reduced to saturation and precipitate ammonium chloride crystals. The ammonium chloride crystallizer can realize the uninterrupted operation of continuous feeding and continuous extraction of material. The crystalline slurry from the OSLO crystallizer is continuously extracted and filtered to obtain ammonium chloride solids. After filtration, the low temperature, low concentration ammonium chloride mother liquor is heated by steam and returned to the final stage of the front-end MVR evaporator for further evaporation and concentration.
Device Features
1. Adopt MVR evaporator, optimize the process, and give full play to the energy-saving advantages of MVR evaporator.
2. The multi-stage ammonium chloride MVR evaporator has a remarkable energy-saving effect on the evaporation and concentration of low-concentration ammonium chloride solutions.
3. The ammonium chloride crystallizer (OSLO type) is used to reduce the electric load of the ammonium chloride MVR evaporator, and the whole system realizes continuous automatic operation.
4. The ammonium chloride produced by the crystallization system has a large crystal size, which is easy to filter and reduces the moisture content of the ammonium chloride product.
Ammonium chloride MVR evaporator material background
Ammonium chloride solution has high solubility, and the boiling point of saturated solution is higher (see the ammonium chloride multi-effect evaporator for solubility data), the solution is acidic, and the selection of equipment is more stringent.
Ammonium chloride should not be crystallized by direct evaporation through the MVR evaporator at high temperature. At this time, the temperature rise of the compressor required is high and the energy consumption is large. Accelerated wear and poor mechanical life.
Although ammonium chloride can be directly evaporated and crystallized at low temperature, the one-time investment in equipment is relatively large due to the high degree of vacuum in the operation. We use ammonium chloride MVR evaporator + OSLO continuous crystallizer (cooling) process to make a good balance between equipment investment and operating cost.