Absolute 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%. After removing most of the impurities such as water, aldehydes and fusel oil in the ordinary distillation section, the ethanol with the highest concentration of 95% forms an azeotrope with water, which is difficult to use The method of ordinary distillation is separated. In order to obtain absolute ethanol, the ethanol must be further dehydrated.
Most of the preheated raw materials are used as reflux to feed from the top of the tower, and the high-pressure tower (250kPa(G)) is used to discharge the material in the vapor phase by means of stripping, and the waste water is discharged from the tower kettle; the ethanol produced by the high-pressure tower enters in the form of vapor phase Medium-pressure tower rectification (200kPa(G)), the top of the tower obtains ethanol vapor (200kPa(G)) with a water content of ~15wt.% into the membrane, and the waste water is discharged from the tower kettle; at the same time, a small part of the preheated raw material is mixed with the permeate Then enter the low-pressure tower (-50kPa(G)) for rectification, and ~25wt.% ethanol feed liquid from the top of the tower is sent to the top of the medium-pressure tower as reflux, and the waste water is discharged from the tower kettle.
1. The high-pressure column adopts the stripping method, which does not require additional condensation and reflux, which reduces energy consumption, and the gas phase products are directly fed into the medium-pressure column, avoiding the need for a large pressure difference between the medium-pressure column and the high-pressure column due to coupled heating ;
2. The low-pressure tower is used as a concentration tower to reflux the ethanol raw material as a medium-pressure tower, and use the economy of negative pressure rectification to further reduce the heat load of the medium-pressure tower. At the same time, the heating load of the low-pressure tower is condensed from the top of the medium-pressure tower supply;
3. The vapor phase products extracted from the high-pressure tower directly enter the medium-pressure tower for rectification, which greatly reduces the heat load of the medium-pressure tower and improves heat utilization efficiency.