Cooling towers

Operation and water management

Forced Draft Cooling Towers

Forced Draft Cooling Towers

Forced Draft Cooling Towers

Forced Draft Cooling Towers

                                                                                                   

Natural Draft Cooling Towers

Small cooling installations

Water Distribution Details

                                                         

                                                                       

1. Fan          2. Drift eliminator           3. Warm water           4. Water distribution  5. Water sprinkling nozzle     6. Fill packing     

7. Air inlet      8. Water pool       9. Cooled water

Packing Materials

Cooling Tower Mass Balances

Water and Salt BalancesA water balance around the entire system is:

M = E + D + W

Since the evaporated water (E) has no salts, a chloride balance around the system is:

M (XM) = D (XC) + W (XC) = XC (D + W)

and, therefore:

XC/XM = Cycles of concentration

= M/(D + W)

= M/(M – E) = 1 + [E ÷ (D + W)]

Windage Losses

Windage losses (W), in the absence of manufacturer's data, may be assumed to be:

W = 0.3 to 1.0 percent of C for a natural draft cooling tower without windage drift eliminators

W = 0.1 to 0.3 percent of C for an induced draft cooling tower without windage drift eliminators

W = about 0.01 percent of C (or less) if the cooling tower has windage drift eliminators

Heat Balance

From a simplified heat balance around the cooling tower:

E HV = C · ΔT · cp

Hv = Latent heat of water evaporation = 2260 kJ/kg

Δ T = Temperature difference top to bottom

Cp = Specific heat of water = 4.184 kJkg-1C-1

Biocides - The Ct Concept

In disinfection, the ability to inactivate microorganisms is a function of both disinfectant concentration and time.

Fractional removal = Cntm

This is generally simplified to Fractional removal = Ct

Ct values have been determined for99.99% virus and 99.9% Giardia removal

http://www.pnl.gov/fta/6_ozone.htmhttp://www.cti.org/downloads/legion_2000.pdf

Chlorine Dioxide ProductionClO2 made from Sodium Chlorite: Acidification of Chlorite5 ClO2- + 4 H+ --> 4 ClO2 + 2 H2O + Cl-Oxidation of Chlorite by Chlorine2 NaClO2 + Cl2 --> 2 NaCl + 2 ClO2Oxidation of Chlorite by Persulfate2 NaClO2 + Na2S2O8 --> 2 ClO2 + 2 Na2SO4From Sodium Hypochlorite and Sodium ChloriteNaOCl + 2 NaClO2 + 2 HCl --> 2 ClO2 + 3 NaCl + H2OElectrochemical oxidation of chloriteClO2- --> ClO2 + e-Dry chlorine/chlorite (laboratory method)NaClO2 + 1/2 Cl2 --> ClO2 + NaCl (solid)