4.2.5 High pressure feedwater heaters
High pressure (HP) feedwater heaters are also generally of traditional form, but are arranged in a horizontal attitude to ensure free gravity drainage of their bled-steam lines and heater-to-heater drainage.
The arrangement of internal components is revised to provide a drains cooling section, involving a part-length of some of the bottom tubes (of the inlet section of the tube bundle) instead of a part-length of all tubes in a vertical heater (Fig 1.69).
A variation on the traditional design of HP heater with its thick hemispherical pressure head, tubeplate and steam shell, is a design based on boiler technology in which inlet/outlet headers and serpentine tubes are all contained within a steam shell, as illustrated in Fig 1.70.
The pressure parts associated with such a design, known as a 'header' type heater are smaller (relative to the thick walls of a hemi-head and tubeplate heater) and are more amenable to temperature changes as a consequence of load change than the traditional type of heater. Furthermore, it can be made in larger capacities than the traditional design. For large unit sizes, a single line of 'header' type HP heaters could be used instead of a double line of hemi-head/ tubeplate heaters, which may yield space and cost savings, depending on suppliers' specific designs and manufacturing costs.