Entrainment BTA Using Variable Speed Pumping at an Estuarine Intake

Variable pumping rates can substantially reduce cooling water flows, and hence entrainment, for load-following and peaking facilities.  The entrainment reductions are, in fact, often greater than the reduction in cooling water flows because entrainment densities are commonly highest at night when demands for cooling water are the lowest.  However, variable speed pumping also changes the temperature of the cooling water discharge.  The benefits of reduced entrainment must be balanced against the potential reduced survival of entrained organisms as a result of higher thermal stress.  Further, the potential effects of the higher temperature of the reduced discharge flow on balanced indigenous communities in the receiving waterbody must also be considered.

 We evaluate the benefits and impacts of variable speed pumping at an existing load-following power station located along the south shore of Long Island.  We considered site-specific engineering constraints on flow reduction along with the effects of increased thermal exposures on entrainment survival.  The assessment demonstrates that variable speed pumping has the potential to reduce entrainment losses from full flow baseline estimates at levels comparable to that of cooling towers at a fraction of the cost, and without jeopardizing the aquatic communities within the receiving waters.