Drought plagued much of the Western and Central United States during 2018. Poor precipitation throughout the winter months led to lower-than-average reservoir and river levels, creating issues for many utilities during the summer months to provide clean cooling and makeup water supplies. Because water is used in all phases of electrical generation, limited water availability can lead to constrained operations or potential facility derate for many power plants.

During the summer months, water levels fall as evaporation and higher usage from municipal utilities and agricultural efforts occur. This span of time also coincides with the optimal run season for most power plants. With higher ambient temperatures and lower water levels, cooling water and makeup water temperatures continue to increase as well. Limited water resources combined with higher total suspended solids (TSS), total dissolved solids (TDS) and biological growth mean that power plants will need to become more resourceful in finding, retaining and utilizing clean water to continue generating without unexpected outages or facility derate. Fortunately, there are options that can help — without requiring major capital resources to complete.

The prefiltration process can provide operational benefits covering a multitude of equipment and systems for once-through cooling systems and for makeup water derived from rivers and lakes. Prefiltering can remove much of the TSS associated with rivers and lakes, removing sediment, vegetation, trash and debris that will damage cooling systems and reduce heat exchange efficiency.  With higher TSS and TDS, water treatment equipment requires more frequent maintenance to maintain optimal performance while experiencing greater stress and upset conditions than the same operation during non-drought and normal water level conditions. Adding prefiltration to your systems can save costs on maintenance and materials, but can easily be justified by helping to keep your facility online during peak hours.

Given the already-large stress levels on local biological systems within the rivers and lakes during summer months, subjecting them to higher-than-normal effluent from a power plant may cause a noncompliance with plant permits or with section 316(a) of the U.S. Environmental Protection Agency’s Clean Water Act. Mobile cooling towers are a viable tool used to successfully mitigate issues regarding section 316(a) and permit limitations. The towers do this by drawing enough mass through a secondary cooling process to bring the overall effluent flow to expected operating levels.  Mobile “helper” towers are cost-effective temporary solutions for meeting effluent limitation guidelines as well as providing additional cooling capacity to limited primary cooling towers for closed systems. Having extra cooling capacity for peak summer months provides reassurance for meeting capacity demands should temperatures spike or should a mechanical failure occur. 

While prefiltration methods do remove most of the larger aquatic life, other substantial risks — algae and microbial infiltration — can threaten the unit(s). Water brought from low level rivers and lakes will be subject to decomposing biological matter and bacterial entrainment that can be harmful to power plant systems and materials. Biofouling within the system can not only limit flow, but can damage materials, especially piping, reverse osmosis membranes and equipment including pumps and heat exchangers, thus causing potential unplanned outages. Evaluation of current chemical injection rates and system shock can provide protection for plant systems against equipment component failure due to plugging or corrosion. However, excessive chemical treatment should be avoided, as effluent and blowdown limitations can be surpassed as well as potential damage to the systems and materials due to chemical attack. 

If you’re considering solutions to address the limited water availability in your power plant, partner with an experienced team that can help evaluate, prepare for and remedy water quality issues caused by drought.

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Bryan Durant is a mechanical engineer at Burns & McDonnell with more than 17 years of experience designing power plants. As the plant improvements mechanical business unit manager, he’s responsible for the identification, development and execution of small operations and maintenance and capital projects.