Two different cooling tower designs are considered for this project. The first design
(Design A) utilizes the same wet-bulb temperature (75°F) and condenser inlet
temperature (75°) as the current design. Whereas the current towers are designed for a
12°F approach, Design A has a 5°F approach, which is the lowest practical value when
taking economic considerations into view as a design approach less than 5°F
significantly increases the required size, and therefore cost of the towers. The heat load
removed by Design A is equal to the increased heat load from the condenser due to
power uprate and the heat load due to the service water system (Qsw in Figure 6). The
purpose of Design A is to produce cooling towers that are capable of removing the
required heat loads from the plant while operating in the Helper or Recirculation Modes
(all or a portion of the cooled water is discharged back to the river) without exceeding
the NPDES permit limitations for a river temperature increase during periods of
operation that could require the plant to reduce power under the current design.
Operating experience at the plant has shown that periods of high wet-bulb temperature
(80°F) and low river flow (1200ft3/s) can cause the plant to reduce power to avoid
exceeding the NPDES permit limitations [9]. The NPDES permit river temperature
limitations for the most restrictive period of May 16 – June 15 are shown in Table 1.