Cooling towers and the environment: an overview
Cooling towers play an important role in the removal of waste heat in power generation. They help to eliminate thermal pollution of natural waters, but may also create other environmental problems, primarily drift and fogging. A method is described for measuring drift, and results are given of recent field tests using this method. The 22 drift tests showed that a drift rate of 0.05 percent is typical for drift eliminator designs used in the industry for the last 20 years. A new generation drift eliminator, where positive drainage and sealing are part of the design, results in a typical drift rate of 0.004 percent of the circulating water rate. Exhaust droplet size ranged from 22 to 2400 micron in diameter. Larger drops are primarily created by drift and moisture collecting on structural members in the tower's plenum and their eventual reentrainment in the exhaust air stream. An evaluation of the environmental effects caused by drift from a salt water cooling tower leads to the conclusion that beyond some reasonable distance, usually within the plant site boundary, drift does not affect the environment. The basic phenomenon of cooling tower fog is explained. Ground fogging from mechanical draft cooling towers is a result of the warm, saturated exhaust air mixing with cold ambient air. Upon cooling, exhaust air becomes supersaturated, forming a visible fog plume. Under worst case meteorological conditions of atmospheric stability, cold air temperature, high ambient relative humidity, and light to moderate winds, the fog plume will disperse very slowly and may extend a significant distance before becoming invisible. Current technology favors a combination wet/dry system for controlling fog plumes. Such systems use a conventional wet, or evaporative type tower, in combination with a dry finned tube heat exchange system.
- OSTI ID:
- 7357645
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
200101* -- Fossil-Fueled Power Plants-- Cooling & Heat Transfer Equipment & Systems
AEROSOL MONITORING
CHEMICAL EFFLUENTS
CLOSED-CYCLE COOLING SYSTEMS
COOLING SYSTEMS
COOLING TOWERS
DROPLETS
ENVIRONMENTAL EFFECTS
MONITORING
OPEN-CYCLE COOLING SYSTEMS
OPERATION
PARTICLES
PLUMES