Efficient allocation of environmental assimilative capacity: the case of thermal emissions to a large body of water

The economically efficient level of environmental assimilative capacity in the case of thermal electric rejected heat discharges to large lakes subject to temperature standards is considered. A mathematical model relating heated effluent flow rate and ''near-field'' temperature is used to determine maximum diffusor port size. Diffusor costs are developed as a function of discharge velocity, port size being given. Cooling tower costs are also developed for comparison with diffusor costs in selecting an optimal level of thermal assimilative capacity. The relationship between this selection process and optimal power plant siting models is outlined. It is shown that arbitrarily fixing discharge velocity at some practical level will tend to bias the results of these siting models toward overly conservative use of thermal assimilative capacity. That is, available capacity will not be fully exploited, and the cost of a given level of power output will be greater than is necessary. (U.S.)