BG1-10 Turndown Limits for Thermosiphon Reboilers

J. W. Palen
2003; rev 09/2010

Although operating thermosiphon reboilers at less than design capacity (turndown) can cause problems, there often are valid reasons for turndown operation. This report discusses types of controls permitting turndown, different flow behaviors caused by it, and the potential for light component stripping due to poor circulation or exit pipe phase separation.

To help members check turndown limits, HTRI has developed equations for minimum recommended heat flux based on bubble rise velocity and for exit pipe separation based on entrainment considerations. In addition, we compare the operating mean temperature difference with a minimum mean temperature based on boiling range and bubble nucleation theory. This report also analyzes typical cases, reviews pertinent literature, and recommends application of the new method in Xist.