(62e) Distillation Tower Startup Following a Plant Revamp with Focus on Reboiler Operation

Change in tower internals, twinning of condensers and reboilers implemented as part of an ethylene plant revamp resulted in different behavior requiring adjustments in startup strategies. Pre-startup work established process targets through the feed rate transition with consideration to a number of commissioning hold point requiring period of operation below turndown. On many towers, turndown requirements at low feed rates can be satisfied by increasing internal vapor/ liquid circulation through higher reboil and reflux ratios. Other towers, such as Demethanizer Pre-Strippers cannot be false loaded and can results in reboiler stall. This paper discusses the pre-startup strategy developed and the challenge encountered in the execution of the actual startup. While the discussion covers towers and associated equipment, it focuses on reboiler transient behavior around a Demethanizer Pre-Stripper and two parallel Ethylene Fractionator. The three towers discussed have different sump/ reboiler configurations.