Improved drum level control for load cycling

The current technique of feedwater generators employs the “3-element” drum level controller. This control scheme works well for steady state operation, or slow changes in load. However, for units required to perform significant load cycling or those subjected to transients due to upsets in the grid electrical generation, the “3-element” drum level control no longer effectively represents the physical process. This paper describes a modified drum level control scheme (US Patent No. 514 8775), utilizing a feed-forward concept which compensates for the mass inventory within the evaporator due to load and pressure effects. The results obtained from a mathematical plant model show that the improvement in drum level response on a significant load change is quite dramatic for the modified drum level control described in this paper