Section 316(b) of the Clean Water Act regulates the potential environmental impacts of cooling water intakes in order to mitigate the adverse entrainment and impingement effects on aquatic organisms. The recently proposed EPA regulations require that power plants currently using once-through cooling systems at the very minimum, evaluate the cost and environmental benefits of retrofitting to wet or dry cooling towers for their next permit application. However, a sound cooling tower retrofit assessment cannot be confined to cooling tower issues alone. Cooling tower backfits significantly affect the entire cooling system and generating capacity. Though the industry still awaits the EPA’s February 2004 final action ruling to clarify the regulations for existing plants, it is clear that acceptable methods of plant compliance with 316(b) regulations will be decided based upon the costs of new technology available, including cooling tower retrofits. A plant not able to meet the tight impingement and entrainment reduction percentages required under 316(b) will be required to consider the cost of retrofitting technologies versus the expected environmental benefit. The EPA has complied standard costs for retrofitting cooling towers that are extremely optimistic and limited in their scope, and thus tend to be far lower than a plant would actually accrue during a retrofit. These EPA costs of compliance are accepted by default in the cost-benefit analysis unless a plant can make a compelling case that their site-specific costs are much higher than EPA’s estimate or are wholly disproportionate to the environmental benefits accrued by such a retrofit. In either case, an overly simplistic and non-comprehensive tower retrofit cost estimate will increase the chances of a plant being required to implement a closed-cooling system retrofit, which in nearly all cases is the most costly and difficult alternative. In addition to constructing a tower, a cooling tower retrofit also alters many parts of the existing cooling system. Typically, a once-through condenser is designed to operate in a siphon circuit using low pressure buried piping under the turbine building. The condenser, along with its piping, would likely have to be modified to be compatible for a conversion to a higher pressure closed-loop system. The retrofit would require installation of new circulating water pumps to provide the additional required head. Portions of the plant’s large diameter circulating water piping systems and intakes must be decommissioned or redesigned to accommodate the retrofit. The critical parts of any retrofit evaluation will be to identify the site-specific modifications required for a conversion with a reasonably accurate estimate of capital costs. An accurate retrofit evaluation must reflect the impacts on all of the circulating water system components along with the adjusted overall performance. Obtaining accurate cost data on the full scope of a retrofit project is difficult due to many factors. There have been only a handful of cooling tower retrofits in the U.S. The experiences from these are mostly inapplicable due to either their small size or unique factors that facilitated the cooling system conversion. The site-specific nature of each retrofit, including the interpretation of a matrix of environmental siting issues, makes cooling system retrofit estimates very complex. Developing an accurate estimate requires a thorough review the existing cooling system design equipment, features & layout. These data are best obtained from a site visit and interviews with key system and operations personnel. Retrofit budgets for this evaluation should not be based on very “generic” cases prepared without regard to site-specific design & operating limitations. Instead, a realistic turnkey retrofit budget is based on a well planned project that confronts the broad scope of a retrofit including the range of site-specific factors. This paper will summarize the art of the retrofit and provide considerations to develop more reliable and meaningful closedcycle retrofit cooling system cost estimates. It will describe the critical characteristics of cooling towers, pumps, circulating water piping, and condenser modifications. It will provide recommendations to produce reasonably accurate evaluations of the seasonal and peak period (energy penalty) effects of the retrofitted cooling system on plant generation. In fact, those conversion costs and the negative effects on plant generation are the key to determining the realistic effects of a proposed retrofit. Finally, it will present the major consequences of trading-off the adverse aquatic environmental impacts with airborne ones from a retrofitted wet cooling tower.
Experimental study on thermal performance in three-flow cooling tower
