Cooling Pond Steam Fog

Abstract

This paper is responsive to needs to describe and predict the environmental effects from power plant cooling ponds. A study was made to determine atmospheric and pond surface conditions required for steam fog to occur from power plant cooling ponds, to define the dimensions of the fog, and to collect data on deposition of ice. Data, collected principally at the 4-Corners Plant over a three-year period, included water surface temperature, ambient meteorological conditions and occurrence and magnitude of steam fog and ice deposition. With strong winds, the fog extended onshore without lifting. With light winds, the fog extended some distance onshore but then lifted to form stratus. With almost calm winds, the steam fog lifted over the pond and drifted downwind as stratus. Steam fog was observed in winds to 28 mph, air-water temperature differences from 21.5° to 68°F and in atmospheric stability categories C, D, E, and F. A fog index number, Ar/(e_s — e_a)°F/mbs, was defined and used for data interpretation, where Ar is temperature of water less temperature of ambient air, e_s is the saturation vapor pressure of the ambient air and e_a is the actual vapor pressure of the ambient air. The probability of occurrence of steam fog as a function of the fog index number varied from 0.04 for an index number less than 10 to 1.00 for an index number greater than 90. From the data, if fog occurred, its extent along the ground was ≥100 feet 88% of the time, ≥500 feet 35% of the time, ≥1000 feet 18% of the time, and ≥5000 feet 12% of the time. If stratus occurred its extent above ground was ≥1 mile 91% of the time, ≥5 miles 55% of the time and ≥10 miles 36% of the time. Measurements showed that steam fog droplet sizes predominate in the 10 micron diameter size. Values of liquid water content up to 0.20 g/m³ were reported. Ice accretion data show build-up rates from 0.23 to 13 mm/hr of rime.