How to prepare large-particle cobalt chloride?Is it feasible to use evaporation crystallization process? Kang Jinghui evaporator editor will talk to you about how to prepare large-particle cobalt chloride.
The current preparation process of cobalt chloride
The existing evaporation method of cobalt chloride salt solution adopts single-effect kettle evaporation, the energy consumption is large, the evaporation to a certain extent is cooled and crystallized, the crystallized mother liquor continues to return to the kettle for evaporation, and the mother liquor in the system is repeatedly heated, cooled and reheated, and the energy loss is very large.
A new process of cobalt chloride evaporation and crystallization
Cobalt chloride evaporation and crystallization new process preheating + evaporation concentration + cooling crystallization process + centrifugal separation process.
1. Preheating
The cobalt chloride solution at a temperature of ≥ 10 °C is pumped into the stock tank, pressurized by the raw material pump and then enters the L-stage heat exchanger for preheating, and then enters the falling film for evaporation after being preheated by the second-stage preheater.
Evaporation Concentration:
Falling film evaporation: the preheated cobalt chloride solution is pumped into the falling film evaporator, and the raw materials in the falling film evaporator tube are heated with the heating steam outside the tube to boil and evaporate, and the raw materials are concentrated and pumped into the forced evaporator; Falling film evaporation can be double-effect falling film evaporation or MVR evaporation; Among them, the cobalt chloride solution was evaporated by double-effect falling film, and the second-effect evaporation was carried out first, and then the first-effect evaporation was carried out. MVR was used to evaporate the cobalt chloride solution, and the first evaporation was carried out first, and then the second evaporation was carried out.
MVR evaporation adopts sequential evaporation method, the material is from the first stage to the second stage, and the double effect adopts the reverse evaporation method, the material from the second effect to the first effect can ensure that the temperature of the concentrated solution is greater than 86 °C, and the material can be dissolved in its own crystal water. [
Forced evaporation: The heat exchanger shell of the forced evaporator is filled with fresh steam, so that the raw materials in the forced evaporator tube and the shell steam are exchanged to evaporate the raw materials, and then concentrated again until the concentration of the chlorinated drill reaches 54-55%, and then continuously sent to the high-level tank by relying on the potential difference
In the evaporation stage, the concentration of the chloride drill is directly increased to 54-55%, that is, all the free water in the cobalt chloride solution except for the crystal water is evaporated, and after the evaporation is completed, due to the temperature exceeding 85 °C, the cobalt chloride is dissolved in its own crystal water, which is basically still in the solution state, which avoids the process of repeated heating, cooling and reheating of the mother liquor, and can evaporate and crystallize all the cobalt chloride products at one time.
The secondary steam generated by the forced evaporator separates the droplets in the water vapor through the separator and enters the shell of the falling film evaporator; The condensate produced by the heat exchanger of the forced evaporator collects at the bottom of the heat exchanger and enters the condensate tank.
In the evaporation process, the free water in the cobalt chloride solution except the crystal water is completely evaporated, so that the primary yield is greatly improved, the treatment cost is greatly reduced, the process makes the boiling point of the solution increase higher, and it is feasible to use the multi-effect method for evaporation.
The secondary steam generated by MVR evaporation enters the respective separator to separate the droplets in the water vapor from the steam to form secondary steam, the secondary steam enters the centrifugal compressor, the temperature and pressure of the water vapor are increased after compression, part of it enters the shell of the falling film evaporator to heat the material, and the other part of the water vapor of higher temperature enters the roots compressor, and after further increasing the temperature and pressure, it enters the outside of the heat exchange tube of the forced evaporator, and exchanges heat with the raw materials in the tube, and the water vapor releases latent heat and is condensed into condensate.
The condensate produced by the forced heat exchanger of the forced evaporator enters the shell of the falling film heat exchanger, and the condensate produced by the heat exchanger of the falling film evaporator collects at the bottom of the heat exchanger and enters the condensate tank.
In the evaporation process, the free water in the cobalt chloride solution except the crystal water is all evaporated, so that the boiling point of the solution rises higher, reaching 21 degrees, far exceeding the capacity of the usual MVR evaporator, so two compressors are used in series to solve the problem of temperature rise, centrifugal compressor and roots compressor can be, complete series and partial series connection can also be realized, considering the first-level investment cost of the compressor's processing capacity, the actual use of centrifugal and roots partial series series method to achieve.
Cooling crystallization: the concentrate sent into the high-level tank is crystallized to obtain crystalline particles;
In the process of evaporating all the free water, due to the higher supersaturation of the chlorinated drill, it may form a piece when it is slightly cooled, and the liquid with such a high supersaturation cannot be directly cooled and crystallized, therefore, in the crystallization process, the ultra-concentrated cobalt chloride solution with a temperature greater than 85 °C to remove the free water is added to the cold cobalt chloride saturated solution (it can be the original crystallized separation mother liquor, or it can be the newly configured cobalt chloride saturated solution, the new configuration only needs to be used once, and it will be reused in the future). In this way, the supersaturation of cobalt chloride is effectively controlled, so as to solve the problem that the supersaturation of cobalt chloride is higher in the process of evaporating all the free water, and it may form a piece when it is slightly cooled, so that the production can be carried out, and the crystals with very large particles are obtained.
Among them, the quality of the cold cobalt chloride saturated solution is 1-5 times that of the ultra-concentrated cobalt chloride solution.
Centrifugal separation: the crystalline particles continuously enter the centrifuge for centrifugal separation, the mother liquor enters the mother liquor tank, and the mother liquor pump is used to pump the mother liquor back to the high-level crystallization tank; Centrifugal separation of solid packaging.
Non-condensable steam cooler, regulating valve, steam-water separator, and vacuum pump form a pressure stabilization system to ensure that the evaporator works at the design pressure to ensure that the evaporation temperature is stable within the range of process requirements.