The heat used in crude glycerol distillation includes water evaporation, glycerol evaporation, direct (live) steam, steam jet vacuum pump and heat loss of equipment medium.
When calculating steam consumption, it is necessary to set crude glycerol concentration, water-dividing evaporation temperature, crude glycerol feed temperature, crude glycerol distillation yield, glycerol evaporation temperature, external pressure during glycerol evaporation, steam pressure, steam condensation water temperature and steam loss of surrounding equipment medium.
Examples: crude glycerol with 80% glycerol was distilled at 1000kg, feed temperature 20℃, water evaporation temperature 90℃, glycerol distillation temperature 165℃, external pressure 40 mmHg, glycerol distillation yield 97% (crude glycerol distillation yield of saponification waste liquid 96%), heated steam 0.8 MPa, steam condensation temperature 170℃, vapor consumption of surrounding media according to 10% time of steam consumption.
From the above basic data;
The amount of water evaporation is 1000×20%=200kg
The amount of glycerol evaporation is 1000×80%×97%=776kg
The amount of residue is 1000-200-776=24kg
The heat required for distilling 1000kg crude glycerol is as follows.
(1)The heat requirement of 1000kg crude glycerol heated from 20 to 90 for water evaporation is as follows:
1000×(90-20)×Specific heat capacity =1000×70×0.8706=60942kcal
200 kg water evaporation needs heat: 200×Heat of vaporization at 90℃=200×545.3=109060kcal
Q1=60942+109060=170002kcal
(2)When crude glycerol is concentrated to the evaporation temperature of glycerol at 165℃, the heat required is as follows:
Q2=800×(165-90)×Specific heat capacity=800×75×0.71=42600kcal
(3)The heat required for glycerol evaporation is Q3=776×heat of vaporization=776×203.7(165℃)=158071.2kcal
(4)Direct steam consumption. When steam distillation is used, direct steam injection can reduce the vapor pressure of glycerol, accelerate the material circulation and improve the heat transfer effect. The amount of direct vapor can be calculated from the relationship between Dalton’s partial pressure law (total vapor pressure equals the sum of the partial pressures of each component) and glycerol’s boiling point at different pressures.
(5)The heat loss of vapor in the surrounding medium is as follows: Q=(Q+Q2+Q3)×10%=370673.2*0.1=37067.32Kcal
