Boiler Feed Pump upgrade needed because of cycling
At the Fort St. Vrain Generating Station in Colorado, greater pump cycling
raised a few concerns. The plant’s original boiler feedwater pumps were not
designed for frequent starts and stops, which created a higher risk of internal
metal parts galling and increased the potential for pump seizure.
Each of the three HRSGs uses two 100% redundant, 10-stage, axially split boiler
feedwater pumps (Figure 2) running at a typical operating temperature of
approximately 260F and pressure of 2,700 psig. By upgrading to composite
materials and eliminating the metal-to-metal contact inside the Fort St. Vrain
pumps, it was possible to reduce the clearance at all of the internal seals—the
wear rings, center bushing, and throttle bushing.
Since the upgrade, plant operators have been happy with the pump. There have
been no issues starting and stopping the pump repeatedly when the plant is asked
to cycle. After two years of operation, there has been no noted increase in
power consumption or decrease in performance of the upgraded pump.
Furthermore, Fort St. Vrain has experienced at least one added benefit.
Previously, boiler feedwater pump motors would bump into and sometimes surpass
their full-load rated amperage during hot summer days. Occasionally, the motors
would overheat and trip. However, with the upgraded pump drawing less current,
it has added a significant safety factor between full load and a tripped pump
when it is needed most.