7 6 Dry Cooling Towers Cooling mechanism Surface

7. 6 Dry Cooling Towers Cooling mechanism: Surface heat exchanger sensible heat only. Usage and Advantages: Plant site close to loaddistribution center, not sufficient cooling water supply. Less expensive to maintain. Not require large amount of chemical. Disadvantage: not as efficient as wet CT higher turbine back pressure less turbine output less plant eff. Dry CT operates only in closed mode. 2 basic CT: Direct and Indirect. รศ. ดร. สมหมาย ปรเปรม

Direct Dry-Cooling Towers Configuration & Flow: Steam header Fined tubes …condensed…Atm air cooled. Forced draft fan. Disadvantage: high vacuum , need large steam duct to reduce Pdrop, limited to small size power plant < 330 MW. รศ. ดร. สมหมาย ปรเปรม

Indirect Dry-Cooling Towers Configuration & Flow: 1 st = Conventional Surface Condenser + Dry Cooling Tower (to reduced Cooling water temperature. ) 2 nd = Direct contact condenser + Dry CT 3 rd = Same as 1 but using Coolant (ie. Ammonia) instead of water. Disadvantage: 2 - Heat exchangers in series high turbine back pressure รศ. ดร. สมหมาย ปรเปรม

Cooling Lakes or Ponds Configuration & Flow: Hot water from condenser is simply dumped in to a Lake. and left to cool Cooling Mechanism: Natural evaporation, thermal radiation to sky (at night). Disadvantage: very low cooling effectiveness need large area. รศ. ดร. สมหมาย ปรเปรม

The lower limit of cooling is the equilibrium temperature, TE รศ. ดร. สมหมาย ปรเปรม

Spray Ponds and Canals Configuration & Flow Spray pond: similar to cooling pond but smaller + Spray canals: Long open canal or series of canal Cooling Mechanism: like wet cooling tower = Evaporation of circulating water. รศ. ดร. สมหมาย ปรเปรม

Evaporation rate effected by: Weather condition, Tdb, Twb, Wind velocity. A simplified governing equation for a spray canals is รศ. ดร. สมหมาย ปรเปรม