The demand for increasing electricity load while conserving locally limited fresh water supply can sometimes come into conflict, especially with the extended droughts, diminishing snowpack and potential future effects of climate change. Since power plant cooling is the major use of water in most plants, the type of cooling system is important. Traditional wet-cooling systems have good efficiency and low cost but high water consumption; dry cooling virtually eliminates water consumption but at higher cost and reduced efficiency. Hybrid, wet/dry cooling systems have significant water savings, improved efficiency and output but with higher cost compared to wet cooling. When compared to dry systems, however, the hybrid wet/dry usually has lower costs. This report presents quantified tradeoffs between wet, dry, and hybrid cooling systems for typical gas-fired, combined-cycle plants operating in California.
The team developed an Excel spreadsheet-based computer tool specifying the design parameters for closed-cycle wet, direct dry, and parallel wet/dry hybrid cooling systems. To compare costs of the cooling systems, annual operating power requirements, annual steam turbine output reductions, resultant annualized costs, and annual water consumption five California sites representing the range of seasonal and climatic conditions were selected. Calculated results for water consumption were summarized as a percentage of all-wet cooling water usage, cost of water saved, and normalized water. Finally, the tool was used to estimate the economic, power production and water conservation trade-offs provided by the selection of preferred cooling systems for future power development in California.
