Author(s): Edward W. Kempema; Steven F. Daly; Robert Ettema
Keywords: No keywords
Abstract: Section 316 (b) of the Clean Water Act requires the Environmental Protection Agency to ensure that the location, design, construction, and capacity of thermal power cooling water intake structures reflect the best technology available to protect fish. Cylindrical wedgewire screens comprise an efficient technology for decreasing impingement and entrainment losses at water intakes. Such screens draw water through a fine mesh at low flow velocities. Though mitigating EPA’s impingement and entrainment concern, wedge-wire screens run the risk of blockage by frazil ice. We review the characteristics of wedgewire intake screens, and discuss how these characteristics make wedgewire screens susceptible to frazil blockage. The same characteristics that make wedgewire screens successful protectors of fish make them efficient frazil collectors. The small slot openings facilitate clogging of the openings by frazil. The large surface area of the screen elements provides a large area for frazil adherence. Limited observations of operational wedge wire screens suggests that airburst cleaning systems may not be capable of clearing frazil adhering to the intake screens. New methods are needed for frazil-blockage control. The writers outline potential options to mitigate frazil blockage at cooling water intake structures using wedgewire screens.