FW can be defined as return condensate + make-up water. It is the high-pressure deaerated (removal of gases like oxygen and carbon dioxide) water supplied to the boiler from which steam is generated. FW has additional significance in SC and USC boilers. In these boilers there is no drum (storage vessel), so FW flow has direct impact on fuel flow, i.e., both FW flow as well as fuel flow have to be precisely regulated to maintain the FW to fuel flow ratio necessary for proper operation of the plant. It is also important because the majority of attemperation water is supplied from FW. There are several design alternatives available.