Method and system for producing potassium chloride by internal circulation brine mixing and cold crystallization

The invention relates to a method for producing potassium chloride by internal circulation brine mixing and cold crystallization. The method comprises the following steps: 1, mixing E brine and F brine to obtain first-stage carnallite and a brine mixing completion solution; 2, decomposing and crystallizing the first-stage carnallite obtain crude potassium and tail brine, wherein the tail brine comprises 2-6% of NaCl, 2.6-3.5% of KCl and 20-26% of MgCl2; 3, purifying the crude potassium to obtain potassium chloride; and 4, adjusting the tail brine by using the brine mixing completion solution to obtain modulated brine, and mixing the modulated brine with F brine to produce carnallite, wherein the deviation between the component of the modulated brine and the component of E brine is less than 5%. According to the invention, a large amount of potassium chloride in the brine blending completion solution is recovered; the adjustment end point of the prepared saline water is more accuratelycontrolled; the recovery