At present, the evaporation process of domestic ion membrane caustic soda has ascending film evaporation process, double-effect descending film evaporation process and three-effect counter-current descending film evaporation process.
As the rising film evaporation process is only one effect evaporation, steam utilization rate is low, heat energy is not reasonably used, the relative gas consumption is high, from the perspective of economic interests, the practicality of single effect rising film evaporation process is restricted.
Double-effect counter-current falling film evaporation is more widely used, three-effect counter-current falling film evaporation process is less used at present, but three-effect counter-current has the advantages of low energy consumption, high steam utilization rate and large equipment capacity, etc., which is a more suitable evaporation technology.
Three-effect countercurrent falling film evaporation process to produce 50% caustic soda in the application of enterprises.
Advantages of three-effect counter-current.
The three-effect counter-flow falling film
Evaporation System makes full use of the heat of the raw steam and the temperature of the 50% caustic soda solution produced by the first-effect evaporator, and twice makes use of the heat of the secondary steam produced by the system.
The steam condensate from the first-effect evaporator is used to heat 36.5% and 41.8% of the alkali produced by the third-effect evaporator and the second-effect evaporator, making full use of the heat from the condensate.
The high temperature 50% alkali produced by the first effect evaporator is used to preheat 36.5%,41.8% alkali produced by the third effect evaporator and the second effect evaporator, so that the temperature of 50% alkali can be lower than 90℃ after the preheating is completed, which makes full use of the heat energy of the high temperature alkali, and at the same time, it can reduce the use of cooling water of the cooler and lower the operation cost of cooling water.
The secondary steam produced by the first-effect evaporator is used as the heating source of the second-effect evaporator, and the secondary steam produced by the second-effect evaporator is used as the heating heat source of the third-effect evaporator, so that the effective use of heat energy is achieved.
The secondary gas condensate from the third-effect evaporator can be used as make-up water for the cold water tower, saving cold water and reducing emissions.
The first-effect secondary gas condensate can be recycled to the water supply room for diaphragm evaporation and tank washing, which not only reduces emissions, but also makes full use of the thermal energy of the first-effect secondary gas, and at the same time can replace well water as pump sealing water, and can be used as tracing heat for the device in winter, which can effectively save water and reduce production costs.
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