System and operating method for removing light oil impurity by methanol rectification

The invention relates to a system and an operating method for removing light oil impurity by methanol rectification. The system comprises a pre-rectifying tower, a first condenser, a second condenser,a first oil-water separating tank and a second oil-water separating tank; and the second oil-water separating tank is arranged at the back of the first condenser, the first oil-water separating tank is arranged at the back of the second condenser, and extraction water is added into condensate of the first condenser and condensate of the second condenser respectively. The amount of the water addedinto the condensate of the first condenser is 5 to 10 percent of crude methanol fed into the pre-rectifying tower, and the amount of the water added into the condensate of the second condenser is 1 t o 5 percent of crude methanol fed into the pre-rectifying tower. By adopting the operating condition of the system, the extraction water is added in back of the condenser and front of the oil-water separating tank by changing the adding mode from the upper part of the pre-rectifying tower; and the water-insoluble light oil impurity contained in the tower top steam is thoroughly separated out underthe condition of not losing the methanol. The invention is applicable to a device for preparing the methanol by using coal and oven gas as raw materials.