The Sherburne Generating Plant of the Northern States Power Company is
located 40 miles NW of Minneapolis. Plant Units 1 and 2 were placed in service
in 1976 and 1977. Proposed Units 3 and 4 of 800 Mw capacity each were
scheduled for commercial operation in the early 1980's.
Proposed design improvements in the circulating cooling water systems.for
Units 3 and 4 involved complex hydraulic flows. To assure performance, hydraulic
model studies were undertaken. This report details the studies of a 1:12 model
which were made at the St. Anthony Falls Hydraulic Laboratory.
In normal operations, heated water from the condensers is elevated to the
top of forced draft cooling towers where it is released to spray downward for
cooling. Start-up during sub freezing weather could lead to damaging freeze-up
in the cooling tower. An added 84 inch diameter temporary cold weather
by-pass drops the 168,000 gpm flow a distance of over 40 feet and requires a
dispersed manifold port system assuring good energy dissipation and a stable,
well-distributed flow into the tower basin. Based on initial model studies,
several small changes were made in the original design to achieve the desired
Flow in the coaling system is maintained by two 5,000 HP pumps drawing
from a pump basin supplied by two cooling towers. The basin serves to route
flow from either or both towers to either or both pumps. There was a concern
that flow asymmetries or vortices detrimental to pump performance might be
generated in the pump basin. Extensive tests at the model pump suction using
pitots and vortex sensors establish that good flow conditions existed for all
routings and no modification of the basin design was needed.
Separate considerations were given to the influence of trash screens and
fire water pumping and the dispersion of additive acid in the pump basin.
Ripken, John; Mendell, Todd.
Hydraulic Model Studies of the Circulating Water System for the Sheburne County Generating Plant - Units 3 and 4.
St. Anthony Falls Hydraulic Laboratory.
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