Anhydrous ethanol is widely used in food, chemical industry, fuel, military industry, medicine and other fields. The concentration of ethanol produced by biomass fermentation is generally 3 ~ 20wt%. When the highest concentration of ethanol reaches 95% after removing most impurities such as water, aldehyde and fusel oil, it forms a azeotrope with water, which is difficult to be separated by ordinary distillation. In order to obtain anhydrous ethanol, the above ethanol must be further dehydrated.
Most of the preheated raw materials were used as backflow feed from the top of the tower, and the steam phase discharge was carried out by high pressure tower (250kPa(G)) in distillation mode, and the tower kettle discharged the waste water. Ethanol extracted from the high pressure column enters into the medium pressure column rectification in the form of vapor phase (200kPa(G)), and the ethanol vapor (200kPa(G) with water content of ~15wt.% is obtained from the top of the column into the film, and the wastewater is discharged from the tower kettle. At the same time, a small amount of preheated raw materials were mixed with osmotic fluid and then entered the low-pressure column (-50kpa (G)) for rectification. The ethanol liquid extracted from the top of the column ~25wt.% was sent to the top of the medium-pressure column as reflux, and the tower kettle discharged the waste water.
1. The high-pressure tower adopts distillation mode, which does not require additional condensation reflux and reduces energy consumption. Moreover, the produced vapor phase products go directly into the medium-pressure tower to avoid large pressure difference between the medium-pressure tower and the high-pressure tower due to coupled heating;
2. The low-pressure tower is used as the concentration tower, and the ethanol raw material is enriched and then reflux as the medium-pressure tower. The economy of negative pressure rectification is utilized to further reduce the heat load of the medium-pressure tower, and the heating load of the low-pressure tower is provided by condensation on the top of the medium-pressure tower;
3. Steam phase products produced in high pressure tower directly enter into medium pressure tower rectification, which greatly reduces heat load of medium pressure tower and provides heat utilization efficiency.