(144c) Controlling Reboilers Heated by Condensing Steam or Vapor

A large fraction of distillation tower reboilers, possibly most, are heated by condensing vapor. Typical examples are steam reboilers, refrigeration vapor reboilers, and heat-integrated reboilers that condense overhead vapor from same or a different tower. For these reboilers, the control valve can be located either in the steam (or vapor) inlet line or in the condensate outlet line. The two methods are different in principle and operation, have different strengths and weaknesses, and require different measures to achieve trouble-free operation.

The selected method, as well as the features added to overcome its weaknesses, is central for good reboiler operation, performance, and tower stability. The literature has some excellent reviews^1,2 on this subject, but these reviews have last been updated three decades ago. Recent excellent sources³ have only partially addressed some of the key considerations. This article aims to fill in the gaps, combining the old knowledge with the recent experiences into a detailed updated guide to the key considerations, features, and practices that can improve reboiler control and operation.