This presentation gives simple understanding of Raw water Treatment in a thermal power plant.

1. By:
Anand Kadali,
Hari Prasad Gollapalli,
Kalyanam Sudheer Kumar.

2. What is Raw Water?
What is the need for treatment of raw water?
Industrial Waste Water
Agriculture
Natural Calamities
Radioactive Wastes
Oil Spills etc.
Characteristics of Raw Water are classified as:
1) Physical Characteristics
2) Biological Characteristics
3) Chemical Characteristics
Physical Characteristics:
1) Colour
2) Odour
3) Temperature
4) Turbidity

3. Biological Characteristics:
1) Viruses
2) Algae/Fungi
3) Animal/Plant Tissues
 Chemical Characteristics:
Organic Inorganic Gases
Carbohydrates Alkalinity Hydrogen Sulphide
Fats, Oils & Grease Acidity Methane
Pesticides Chlorides Oxygen
Phenols Heavy Metals
Proteins Phosphorous
Surfactants Sulphur
Toxic Compounds

4. Impurities present in river water can be classified into:
1) Suspended Solids (Dirt, Silt, Mud, Plankton, Coloured Organic Matter)
2) Iron & Dissolved Solids (Calcium, Magnesium, Iron, Nitrate, Chlorides, Silica &
Sulphates )
3) Dissolved Liquids & Gases (CO2, NH3, o2, Hydrogen Sulphide & Oils)
 RAW WATER INTAKE SYSTEM:
Koradi TPS: IEPL BELA TPS:
No. of Raw Water Intake pumps=7 No. of Raw Water Intake pumps=3
(6 running / 1 standby) (2 running / 1 standby)
Motor ratings: 6.6 KV, 1000 KW Motor ratings: 440V, 180A (max)
Discharge capacity: 15000 cubic meter/hr Discharge capacity:1200 cubic meter/hr

6. Screening:
To prevent floating material of fairly large size.
Coarse Screens made of steel bars of 25mm diameter spaced about 100
mm
Apart are provided to restrict the entry of any floating material.
Fine Screens are normally fitted immediately after coarse screens of order
6mm.

7. Pre Chlorination:
Chlorine is injected into raw water at a dosing rate of 2-5 mg/liter.
Pre chlorination destroys bacteria & kills algae.
 Oxidizes and precipitates iron and manganese.
 Reduces color and slime formation.
Raw Water Storage:
Raw Water stored as a backup of 7 to 8 days in plant’s reservoir.
This is sufficient to reduce pathogenic bacteria, suspended solids
& river algae.
Raw water quality is noticeable purely as a result of retention of
water provided.

8. Aeration:
Gases are absorbed or liberated from water.
Excess CO2 and H2S are lost.
oxygen is picked up from atmosphere.
Volatile substance liberated by algae growth or decomposing organic
matter can be released out.
 Fe & Mn are oxidized and precipitated out.
Taste , Odour and Corrosion Properties of water can be maximum controlled.

9. Coagulation:
A process by which small particles in suspension join together to form
larger agglomerate. Fine suspended particles and colloids carry positive
& negative charges.
For agglomeration fine particles should come in contact with each
other. Mixing promotes the effect but violent mixing breaks down the
attraction between the particles.
Coagulation Aids Poly Acryl amide
Activated Silica

10. Flocculation:
Aluminum & Iron Salts gives good flocks normally slight acidic pH.
5-6 pH for Fe and 6-7 pH for Al.
Al2(SO4)3+6H2O Al(OH)3+3H2SO4
When pH of water come down below coagulation pH, then Lime Ca(OH)2 is
added to raise the pH level.

11. Clarifiers:
Water is cleared from most of the suspended particles. It consists of a
flash mixer & settler in separate compartments.
Flash Mixer Chemicals dozed + high speed agitation + retention
Flocculation Chamber Gentle agitation + 20-60 minutes
retention.
Settling Chamber Collection of suspended particles.

12. Filtration:
Rapid Sand Filters consists a bed of graded sand of 30mm to 15mm mesh
about 0.6m depth and gravel sizes of 2.5mm to 25mm.
The filter operates between 5-10 cubic meter/Hr and capable of removing
particles of size 10 microns.
The filter are designed to backwash once/twice a day by filtered water
only .

13. Activated carbon filter :
Granular carbon is used as a filter bed through which water is passed.
Limitations of ACF:
Filtration is a slow process.
Bacterial growth
 Cl2 + H2O 2HCl + ½ O2

14. Conclusion:
Thus after the filtration process the water is stored in a filtered water
storage tank and this water is called portable water/general service water and
suitable for drinking and cooling of some auxiliaries and other purposes. This
water is further sent to post treatment in DM Plant.