Pure Steam Generators separate dry steam from impurities as the critical purification step. PSGs characteristically have to meet a highly fluctuating demand – autoclaves need output to respond from zero to maximum within a few seconds, without appreciable pressure drop. Thermo-syphon re-boilers offer the most favourable response, maintaining a large reservoir of water superheated to the required temperature and pressure, ready for instantaneous call-off without elaborate feedwater pre-heating.
For use with saturated steam autoclaves, removal of non-condensable gases is an additional critical process parameter. Alternative methods include de-gassing in a feedwater breaktank, or stripping out ncg’s from the feedwater as it enters the column.
Pure steam can be delivered from the first column of a multi-effect still, although in this case the delivery characteristics are better suited to steady-state demand.
