Efficiency Scaleup Process Factors

This section focuses only on process scaleup— i.e., scaling up from one chemical system to another, and also scaling up from one set of process conditions to another using the same system. Equipment factors such as column diameter, operating regime, and tray geometry are considered separately in the following section. 

Different type of system. Sections 7.3.1 and 7.3.4 suggest that if liquid viscosity, relative volatility, surface tension, and surface tension gradients are similar, one can expect similar efficiencies. Since it is difficult to attain similarity in all these, it is best to scale up from the same chemical system. Further, in aqueous-organic systems where surface tension gradients can be steep, concentration has a marked and unpredictable effect on efficiency U16,184,187). Data collected in one concentration range may scale up poorly to another. 

One type of system scaleup which can be done with confidence is extending efficiency data from one press lre to anoth. The small increase of efficiency with pressure (Sec. 7.3.4) can be allowed for usii% the O Connell correlation (Sec. 7.2.2). Caution is required when going to high pressures ( 150 psi), as vapor recycle may reduce efficiency, and this effect is difficult to predict. 

Different process conditions. Here we discuss staying with the same system, but extrapolating test data to different process conditions (e.g., feed composition, reflux ratios, feed temperature, etc.). Concentration and pressure effects were discussed separately above flow regimes are discussed separately in the next section. 

In plant or pilot tests, separation data are analyzed by computer simulation that reproduces test conditions. The number of theoretical stages in the simulation is varied until the simulated product compositions and temperature profile match those measured. Truy efficiency is determined from the number of stages that give a good match to test data. 

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