A differential algebraic model for the simulation of thermosiphon systems

Abstract

The main alternative employed for the reboiler in distillation towers is the thermosiphon. In this case, the flow circulation does not depend on the existence of a pump, the flow is promoted by the difference in the density between the liquid column inside the distillation tower and the two-phase stream along the heat exchanger. Despite its importance, few papers have presented a full analysis of the simulation of this kind of system. In this context, this work discusses a differential algebraic model for the simulation of vertical thermosiphons. The model describes the behaviour of the entire hydraulic system, encompassing the feed piping, the heat exchanger and the return pipe to the column. The model is composed of mass, momentum and energy balances. The vaporizing stream can be composed of any number of components. Transport parameters for each phase are evaluated using proper correlations. The resultant mathematical model is composed of a set of differential algebraic equations. The application of the proposed approach is illustrated using a typical reboiler example.