Entransy dissipation based optimization of a large-scale dry cooling system

The natural draft dry cooling tower (NDDCT) with heat exchangers accounts for about 10 percent of the total investment of a power plant, so it is meaningful to optimize the geometric parameters to explore the potential that matching the cooling load of a power generating unit in the most cost effective way. The entransy dissipation equations of two typical irreversible heat transfer processes, including that the ambient air heated by heat exchangers and circulating water heated by the exhausted steam of turbine, are derived in this paper. Combined with the force balance equation of NDDCT, all parameters that may affect the performance and annual cost of a cooling system are took into consideration. Such constituted constraints are applied to the Lagrange multiplier optimization of such a system. Based on the mathematical relation and conditional extremum method, an optimization equation group aiming to obtain the minimum of total annual cost is constructed. Finally, a practical 600 MW power generating unit is taken as an example to illustrate the applications of entransy dissipation based optimization principle. The result indicates that total annual cost of the dry cooling system can drop from $6 420 643 to $5 665 660.