Northern States Power Company's Black Dog Power Generating Plant discharges
its condenser cooling water into a pond called Black Dog Lake, which
releases it through two outlets into the Minnesota River. In this study
it was found that an average 63 percent of the heat load rejected by the plant
was dissipated to the atmosphere by the lake during a period from March
1974 through January 1975. Daily heat dissipation varied from 15 to 128 percent
because of temporary heat storage in the lake (lag) under transient
weather conditions. Daily lake effluent temperature fluctuations were determined
and compared to Minnesota River temperature fluctuations. The lake
very effectively reduces the impact of thermal discharges on the Minnesota
River. Its effectiveness was found to vary with season, with a maximum in
midsummer and a minimum in midwinter, presumably due to sinking plumes. A
mathematical model of the unsteady well-mixed type predicts summer effluent
water temperatures well, but is not applicable for winter conditions.
Stefan, Heinz; Nguyen, Chau.
Waste Heat Dissipation and Effluent Water Temperatures from Black Dog Lake.
St. Anthony Falls Hydraulic Laboratory.
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