Thermosyphon reboilers provide a simple, low-maintenance design for distillation tower reboiler systems. Design of true thermosyphon exchangers requires an intimate knowledge of a distillation tower's heat balance, temperature levels, and pressure balance in the reboiler loop. Depending on system relative volatilities, the temperature levels vary strongly with composition gradients. This paper compares the commonly used simulation networks for different thermosyphon exchanger-distillation tower configurations. The implications on exchanger design of the correct and incorrect simulation configuration will be shown in case studies of two industrial units. The two cases compare a low relative volatility (alpha) system (ethylene-ethane splitter) and a high alpha system (fluid catalytic cracking unit deethanizer). Main factors presented include impact on equipment size and design. Proper design criteria for the simulation of the thermosyphon exchanger and distillation tower and for integrating process and equipment design are shown.
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