Design of Distillation Plants

Rectification is by far the most widely used separation process in the chemical industry. It is characterized by robust technology that is not prone to disturbances and has comparitively low investment costs. The energy requirement is, however, considerable. About 40% of energy consumption in the chemical industry is used for distilla-tive separation. Therefore, integrated energy measures for multiple use of the thermal energy are of special importance and are widely used (see Section 6.1.6.2) [Kaibel 1990]. 

Short-cut methods and graphical procedures such as the McCabe-Thiele method have declined in importance, since the combination of computer programs with material databanks allows rapid treatment of distillation processes. 

For an overview approximation and dimensioning, the relationships of Fenske and Underwood can be used to determine the minimum plate number N j and the minimum reflux ratio (Equations 2.3.2-26 and 2.3.2-27)  

By definitioii the Fenske equation for the minimum plate number only applies for plate columns with a plate efficiency of unity. The use of this equation for packed columns leads to considerable errors, especially at high relative volatilities. The minimum plate number of packed columns shoul be calculated with Equation 2.3.2-28  

Economic designs result for plate numbers that are about 1.3 times the minimum plate number or 1.2-1.3 times the minimum thermal power. With regard to controllability and the minimum trickle density, the reflux ratio should not be less than about 0.3-0.5. 

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