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Cooling Water Treatment

TREATMENT

FOR

Chlorination Controlling Microbiological fouling
Filtration Prevention of fouling of heat transfer surface.
Sulfuric acid Regulation of pH

CHEMICAL DOSING SYSTEM

Inhibitors Protection of Metal from Steel/Copper corrosion.
Antiscalent Precipitation of Alkaline earth salts
Antifoulant Retarding deposition of corrosion products.

Reasons of fouling
Silt introduced by the make up water.
Dirt from air.
Reaction of residues from chemical treatment.
Microbiological debris.
Products produced by corrosion such as hydroxides and insoluble salts.
If fouling is not controlled, it will result in heavy deposits inside cooling water tubes, resulting in reduced tube diameter.
Fouling is controlled by side stream pressure filter/ Chlorination/ chemical dosing

SELECTION OF CAPACITY OF SIDE STREAM FILTER

% of reduction of undissolved solids.
( select 80%)
t = Time desired for reduction in hrs.
(Select maximum in 48 hrs. )
b = blow down rate m3/hr
v = Total volume of cooling system M3
 
f = Side stream filtration rate m3/hr Example

For V = 6000 M3, t = 48 h,
b = 100 M3/h
Filtration rate = 100 M3/hr

MICRO - ORGANISM

Bacteria, algae & fungi present in cooling water circuit decreases the efficiency of heat transfer in cooling tower and condensers.

Chlorine is the most widely used chemical in industry as oxidizing agent for destruction and dissolution of micro-organisms.

Chlorination is effective only when cooling water pH is between 6 and 7.

COOLING WATER
pH

% of HOCl for
effective oxidation

RECOMMENDED DOSAGE

6 97
Free residual chlorine of minimum 0.5 ppm is recommended after meeting chlorine demand in C.W. sample analysis.
7 76
8 24
9 3
At pH 7 in C.W. System every 1 ppm Cl2 dosed only 0.76 ppm is used as oxidizing agent for control of micro organism.

GENERAL GUIDELINES FOR CHLORINE DOSE OF REASONABLY GOOD COOLING WATER.

CW system Estimated Chlorine dosage - ppm
Once thro' inland Lake / River Water / Sea water Continuous dosing 1 to 2 ppm + shock dosing 3-5 ppm for 15 min. for every 8 hr. Cycle.
Recirculation CW system (inland / Sea water) Continuous 1-2 ppm Shock 3 to 5 ppm
Make up water for CW circulation water Continuous 1-2 ppm

CALCULATION OF H2SO4 DOSING SYSTEM

CW CIRCULATION RATE 34000 m3/hr (H2SO4) DOSING REQUIRED

= 88.4 kg/hr @ 98%

COOLING êT 18OF

DOSAGE QTY. @ 30 OC

MAKE UP WATER @ 2% = 680 m3 /hr H2SO4 % Sp. Gr
 
Dosing (LPH) for
88.4 kg/hr
Selected
Pump
M. ALKALINITY TO BE MAINTAINED 150 PPM

98%

1.8261

48.4

100 LPH

M. ALKALINITY OF MAKE UP 140 PPM

As the selected Dosing Pump of 100 LPH can meet 200% of the required dosing rate.

CYCLE OF CONCENTRATION 2
QUANTUM OF M. ALKALINITY {(140x2)-150} = 130 PPM
COOLING WATER CHLORINATION SYSTEM FOR INLAND CT CIRCUIT

GAS CHLORINATORS

ELECTROCHLORINATORS

Type of Chlorine dosing Shock Dosing of Cl2 once in 8 hours
IEC FABCHEM LIMITED Provides a reliable (Electrochlorinators) Chloridose Generator to produce Sodium Hypochlorite at site using common salt, AC power supply and water. A dosing pump is used to dose
the Chloridose solution.

To meet the requirement of cooling water supply IEC offers various chloridose models.

The micro organisms are killed by the NaOCl produced using only common salt, power and water.
Cooling Water circuit Recirculating type
Make up water Flow Rate 456.3 m3 / hr
Circulation water flow rate
in Cooling Tower
24,000 m3 / hr
Chlorine Shock Dosing rate  5 ppm
System (hold up) volume 4000 m3
Duration of shock dose
( one cycle time )

System Volume
Circulating Rate=

4000
24000

10 minutes = 0.167 hr Amount of Chlorine dosed/day 132 kg/hr for 1/2 h
= 22 Kg/shift (66 Kg/day)
Rate of chlorine dosing
& Capacity of Gas
Chlorinator

5 (ppm) x 4000 x 1
1000 x0.167
132 kg / hr

Capacity of the plant
of Electrochlorination
66 kg/day
22 hr Operation
3 kg/hr.
Shock dosing is effective only when 5 ppm
is dosed in one cycle time.
( 10 min = 0.167 hr for the above )
By selecting an electrochlorinator of 3 kg/hr the capacity hypochlorite solution of 8 gpl concentration is generated and stored for 7 hrs 50 min and the stored solution is dosed in 10 minutes. This will give an effective chlorine dosage of 22 Kgs/shift. (2750 lit of 8 gpl sod. Hypochlorite solution per shift)

To produce Equivalent of 1 kg of chlorine Electrochlorinator consumes 3kg of common salt and 5 kw of AC power
Dosing time as specified is 0.167 hr.
The volume of 4000 m3 is dosed
@ 5ppm in 0.167hr
Frequency of
shock dosing
3 times a day for 10 min
Amount of Chlorine
dosed/day
132 kg/hr for 1/2 h
= 22 Kg/shift (66 Kg/day)
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