(131a) A Methodology for Predicting the Performance of Batch Strippers in the Mass Transfer Limited Regime

Batch stripping of volatiles from liquids are employed widely in chemical industry in the form of simple stirred tanks with a stripping agent such as steam or nitrogen sparged below the agitator. The main advantages of such batch stripping units are: low capital cost and less complex operation, when compared to packed columns or other forms of continuous stripping units. Irrespective of the mode of operation, it is a challenging exercise to model and accurately predict the performance of stripping operations particularly in the mass transfer dominated regime, for example when stripping volatiles from highly viscous fluids. An equilibrium based approach in this case is not applicable and fails if used for predicting the stripping performance. It gets even more complicated to model a dynamic process such as a batch stripper where temperature, pressure (vacuum), stripping agent flow rate and volatiles composition can all change with time.

In this talk, we demonstrate a methodology for predicting the performance of dynamic plant scale batch stripping operations using simple lab experiments combined with the concepts of stripping factors and transfer units. Stripping volatiles from a commercially produced polyol in a 9000 gallon batch stripper is used as a case study. A concept of instantaneous stripping factor is used to gauge the stripping power at any given point of time. This is combined with the number of transfer units obtained from the volatiles concentration in the liquid phase before and after the stripping operation. A functional relationship between the two is established using lab scale experiments, which is then used to accurately predict the performance at the plant scale, as demonstrated in this study. Such an approach can be used to design new stripping operations or for rating existing ones for potential improvements.