I am working in 266MW Coal fired Power plant. We have problem to control drum level during BFP Runback (one BFP operation). For information, we have 3 BFP and one is standby.
During BFP runback, Unit load demand is decreased to 133MW and BLR Master demand and TBN master demand will be changed from Unit load demand.
As BLR reaction is slow to follow BLR master demand, coal firing condition is still in same condition (=drum output high!), but BFP has already been tripped. So Drum input is low!
Due to this problem, Drum level cannot be maintained at 0mm (set point) and feed water level control valve is opened from 55% to 63%. During this time, remaining one BFP is trippped due to over rated flow. (rated flow: 490t/h, BFP runback: 530t/h)
How can I operate one BFP during runback to satisfy drum level and
BFP overcurrent trip condition?
If there is typical logic for BFP runback and drum level control, please let me know.