What is methanol distillation process?

At present, domestic and foreign methanol plants use the distillation method to refine crude methanol.The commonly used processes are mainly two-tower processes (single effect) and three-tower processes (double effect). The mechanism of the two rectification processes is the same,and the main difference is the setting of the main rectification tower and the comprehensive utilization of energy.

(1) Two-tower process

The two-tower process is a common method for refining crude methanol. The first tower is the pre-rectification tower, the second tower is the main rectification tower, and the low-pressure steam is used as the heat source in the two tower reboilers.

The pre-rectification tower is used to separate the light components and dissolved gases (H2, CO, CO2, etc.), while the main rectification toweris used to remove the repeated components and obtain the refined methanol product.The crude methanol containing water and high boiling point components enters from the middle of the tower, the higher alcohols is drawn from the side line below the feeding plate,the water containing trace methanol is discharged from the bottom of the tower, and the product refined methanol is removed from near the top of the tower.

(2) Three-tower process 

The three-tower process is also widely used, especially in large installations with strong competitiveness.The difference with the two-tower process is that two main distillation towers are used, the first main distillation tower pressurized operation, the second main distillation tower atmospheric pressure operation.Using the condensation heat of the top gas of the pressurized tower as the heat source of the bottom reboiler of the atmospheric tower, which not only saves heating steam, but also saves cooling water, and effectively uses energy.

The operation of the pre-distillation tower is similar to the process of the two towers, the methanol-water mixture from the bottom of the pre-column is fed into the first pressurized main rectification column through a booster pump, and the reboiler is heated by low pressure steam. The top gas is introduced into the reboiler of the second atmospheric main rectification tower, and the gas condensation heat is used as the heat source of the second tower.The methanol-water mixture discharged from the bottom of the first main rectification tower enters the second main rectification tower by using the pressure difference to remove the water and components impurities. The high grade alcohol is extracted from the side line of the tower, and the waste water at the bottom of the tower contains about 0.5% methanol. The refined methanol of the product is partly extracted from the top condensate of the first main rectification tower and partly from the top condensate of the second main rectification tower.

According to the analysis results, it can be seen that the process indexes of the two basic processes of methanol rectification are basically the same. The three-tower process uses double-effect rectification to reduce the consumption of cooling water and steam, so the equipment investment is high and the operation control is complicated. The two-tower process uses single-effect distillation, and the consumption of cooling water and steam is high, so the equipment investment is low and the operation control is simple.