At present, the falling film evaporation process is widely used in the production process of potassium hydroxide flake alkali. When the potassium hydroxide solution enters the falling film tube of the falling film evaporator and falling film concentrator, it forms a uniform liquid film along the inner wall of the heating tube and falls by gravity for heating and evaporation.
Outside the heating pipe of the falling film evaporator, 0,9mpa low-pressure steam from the external pipe network and the secondary steam generated by the falling film concentrator are used for heating. Outside the heating pipe of the falling film concentrator, molten salt is used for heating. Through indirect heat transfer and vacuum negative pressure technology, the temperature of potassium hydroxide solution is gradually increased, so as to achieve boiling. The water in the solution is partially evaporated, and molten 90% ~ 95% potassium hydroxide can be obtained, which is cooled and scraped by the rotating drum of the flake alkali machine, Enter the finished product packaging.
The caustic soda will enter the production system for a long time, and the caustic soda will be oxidized on the surface of the equipment, which will inevitably lead to the corrosion of the lower caustic soda production system. Therefore, the number of shutdown shall be reduced as much as possible to prevent the frequent startup and shutdown from aggravating the corrosion of the equipment and shortening the service life of the equipment.
In the production process of KOH flake caustic soda, there are external process conditions such as low-pressure steam from public works, natural gas, nitrogen, circulating water, cooling pure water, production water, plant air (compressed air), instrument gas, etc. any interruption or even instability will lead to the production shutdown of flake caustic soda system, and its own process operation failure, equipment operation failure, instrument control failure, electrical operation failure, etc, Sometimes it will also become a key factor in system shutdown.
In order to ensure that the potassium hydroxide solution can form a uniform liquid film in the heat exchange tube of the falling film evaporator and prevent the thermal stress corrosion of the column tube caused by the formation of dry wall area due to the fracture of the liquid film, the low load is required to be no less than 30% of the design load. In normal production, it is required to be put into production within the range of 60% ~ 100% of the rated output; During the start-up feeding, it is not suitable to feed too much to prevent the alkali liquor from forming a film or the film is too thick in the row pipe due to too much feeding, the water in the alkali liquor is not completely evaporated, and the concentration process cannot be carried out well. At this stage, too large or too small flow will corrode the nickel material, damage the equipment and increase the nickel content in the sheet alkali.
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