Hydrodynamic Characteristics of Deaerator Head Drains Subject to an Adverse Differential Pressure

Abstract

In some power plant deaerators, water is required to drain freely from the heating/deaerating head via vertical pipes into the storage tank, sometimes against an adverse differential pressure. The situation is shown to be complex in that six possible discharge regimes are possible, three of which are unstable. Unstable discharge results from steam breakthrough leading to the build up of sloshing water in the head, intermittent discharge and possibly head tray damage. Unstable discharge may also provide an explanation for the noise and vibration associated with deaerators, particularly during abnormal operation. Data and correlations are presented to enable the stable and unstable regimes to be identified and critical differential pressure to be calculated over a range of drain/drum radius ratios from 0.08 to 0.25. This in turn allows instability to be avoided or ‘designed-out’, as shown in a worked example.