The invention discloses a segmented cooling
system and method for evaporating and crystallizing
fly ash water washing liquid to obtain
sylvite, and belongs to the field of
fly ash water washing liquid treatment. The
system comprises a pretreatment and
evaporation sodium separation unit, a vacuum
flash evaporation cooling unit, an indirect heat exchange cooling
crystallization unit and a separation
drying unit which are in fluid communication in sequence, the vacuum
flash evaporation cooling unit adopts a structure without a heat exchange wall surface and is matched with a condensation
system capable of recycling
heat energy; and the indirect heat exchange cooling
crystallization unit is matched with a
forced circulation and external heat exchange structure. According to the method, a segmented process of vacuum
flash evaporation precooling and indirect heat exchange deep cooling is adopted, firstly, the
potassium-rich
mother liquor at the temperature of 100-110 DEG C is cooled to 55-65 DEG C through vacuum flash
evaporation, and then is cooled to 20-30 DEG C through indirect heat exchange, so that
potassium chloride is fully crystallized. According to the method, the
energy consumption of a vacuum system can be reduced by 30-50%, scaling of a high-temperature section is eradicated fundamentally, the product purity is guaranteed to reach 90% or above through a flash
evaporation precipitation-cooling redissolution self-purification mechanism, and efficient, low-consumption and long-period stable
recovery of
potassium chloride in the
fly ash water washing liquid is achieved.