Hybrid Cooling System Thermodynamics and Economics

Wet cooling towers can be used as helper systems with once-through cooling at river-side power-plant sites where the permissible river heat assimilation capacity is inadequate to absorb all of the waste heat. A comprehensive computer model is used for the thermodynamic analysis, economic assessment, and optimum design of once-through/wet tower hybrid cooling systems. Several different configurations are investigated, and results are presented for an 1,150 MW nuclear power plant located on the Missouri River at Sioux City, Iowa. The hybrid cooling system arranged in a series water path with a partially closed-cycle loop appears to be the most economical configuration for the site conditions studied when zero water costs are used. Comparison of hybrid systems with once-through cooling and closed-cycle wet tower systems indicate that hybrid cooling systems are economically superior. A trade-off function between total cost and water evaporation is presented to indicate the best hybrid arrangement for sites where water availability is limited.