Typical treatment process of high salt wastewater
Zero emission core process——Evaporation concentration、Evaporative crystallization
Evaporation concentration: to obtain a concentrated solution for direct use as a chemical product or semi-finished product; Concentrate a solution to a saturated state for crystallisation operations to obtain a solid solute; Remove impurities to obtain a pure solvent.
Evaporative crystallisation: The process of crystallisation in which a solute crystallises from a solution in two steps. The first is the formation of crystal nucleus, first of all to produce microscopic grains as the core of crystallisation, this core is called crystal nucleus. The second is crystal growth. After the crystal nucleus is formed, the crystal nucleus grows up and becomes a macroscopic crystal. This process is called crystal growth. Both the nucleation process and crystal growth process are driven by the supersaturation of solution, primary homogeneous nucleation, primary heterogeneous nucleation and secondary nucleation. Secondary nucleation is mainly contact nucleation. Nucleation in industrial crystallisers mostly belongs to contact nucleation, which occurs under the condition of containing crystals of the crystallised substance in solution.
Introduction to common evaporator
Single effect evaporator
When the solution evaporates in the evaporator, the secondary steam generated is no longer used, then the evaporation operation is called single-effect evaporation. The evaporator using single effect evaporation method is called single effect evaporator.
Multiple evaporators will be connected in series, and the secondary steam will be passed to another evaporator with lower pressure as heating steam, so that the heating steam can be used for many times in the evaporation process.
Single effect evaporator
Multi effect evaporator
Mechanical Vapor Re-compression
MVR is the abbreviation of Mechanical Vapor Re-compression (i.e. Mechanical re-compression of steam). Its principle is to use Mechanical compressor to re-compress the secondary steam after evaporation to improve its enthalpy value, and then send it back into the heating chamber as a heat source to heat the incoming material, and then release its own heat and transform into condensed water. The heated material is vaporised and condensed before being discharged from the system as the final product. The theoretical basis of MVR is derived from Boyle's law. So PV over T is K.
According to this principle, when the thin secondary steam after volume compression, its temperature will increase and the pressure will increase, so as to realise the low temperature and low pressure steam into high temperature and high pressure steam, and then can be used as a heat source to heat the original liquid to be vaporised, so as to achieve the purpose of recycling and utilising steam.
In the evaporation process, thin materials are added from the top of the evaporator, and the liquid film formed is in the same direction as the steam flow, descending from the parallel flow up and down. Suitable for high concentration, high viscosity materials; Not suitable for materials that are easy to crystallise.
Forced circulation evaporator
High cycle speed; It can be used for evaporating materials with large viscosity and easy crystallisation and scaling; Large heat transfer coefficient. The heating chamber is acted by the tubular heat exchanger, which is the heating unit of the evaporation system. The heat exchange tube is completely immersed in the solution and driven by the circulation pump as the power. The material is featured by large flow circulation flow between the heater and the evaporation chamber.
Falling film evaporator
Forced circulation evaporator
Introduction of common crystalliser
Freezing crystallisation system mainly by the cooler, the cooling crystalliser, cooling circulating pump, cooling mould as the centre back feeding, sodium sulfate crystals from cooling mould top subsidence, ensure enough time, to ensure that the sodium sulfate crystal growth enough size, at the same time in cooling mould design special overflow plate, to prevent the sodium sulfate crystals with the upper from mother liquor. After the cooling crystalliser mother liquid is heated through the pre-heat exchanger, it is returned to the sodium chloride thermal crystallisation system again.
According to the different freezing points between substances to be separated, partial crystallisation is achieved by gradually reducing the temperature of the initial liquid mixture. The solid phase precipitated from crystallisation has different chemical composition from the residual liquid, so as to achieve the purpose of separation and purification. Crystallisation process is the melting liquid temperature in the process of gradual decline, a component in the molten crystallisation liquid in a supersaturated state, began to tuberculosis, and gradually grow into crystals, crystals in the process of increasing, the inevitable mother liquid impurities encapsulated in crystals, coarse crystals through the process of sweating purification.
Vacuum cooled crystalliser
A hot, saturated solution is added to a crystalliser insulated from the outside world. Because of the high vacuum maintained in the crystalliser, the boiling point of the retained solution is lower than the temperature at which the solution was added. Thus, when the solution enters the crystalliser, it is cooled by an adiabatic flash process to an equilibrium temperature corresponding to the pressure in the crystalliser.