The water available from different water sources cannot be used directly in boilers as such. The objective of water treatment plant is to produce the boiler feed water so that there shall be:
- No scale formation
- No corrosion
- No fouling
The treated water is called ‘De-mineralized Water’ and the plant where it is treated is called Water Treatment Plant.
Process Sequence of Water Treatment Plant
Water from river
↓
Flash mixer
↓
Clarifier
↓
Filter pack
↓
Clarified water tank
↓
Softening plant
↓
Soft water to various units
Step Discussions:
Water from river:
Water comes from various rivers in water treatment plant.
Flash mixer:
In this segment Al2 (SO4)3, polymer etc are mixed in water.
Softening plant:
In this segment activated carbon are used as a softener.
Soft water to various units:
After softening of water it is supplied in various units for various purposes.
There are two types of water are prepared in water treatment plant:
- Clarified water for washing purpose.
- Soft water for dyeing purpose.
Chemicals are Used in WTP:
- Aluminum Sulphate
- Polyelectrolyte
- Sodium Chloride
Amount of Chemical Used:
- Polymer- .1% solution
- Al2 (SO4)3- 10% solution
- Lime- 10% solution
Experiments Performed in WTP:
- Total hardness test
- Jar test
- pH meter test
- Titration for chlorine content test
Requirements of WTP:
The importance of maintaining supply of high purity water for Boiler purposes in Thermal power stations is well recognized. The presence of undesirable contaminants in water exceeding the few PPB level may lead to serious consequences.
The requirements of pure water have been met by recent developments of improved ion exchange resins and regeneration techniques.
The need for removal of dissolved solids from water arises under several situations. These range from effluent water treatment, water purification for portability, treatment as boiler feed and other industrial applications.
Why Water Treatment is Required?
If proper treatment is not done for water then Corrosion, Scaling, Microbiological contaminants and fouling will occur in the system.
a). Corrosion:
It is an electrochemical process by which a metal returns to its natural state. For e.g. Mild Steel is commonly used metal in cooling water systems and is very susceptible to corrosion. It will return to its iron oxide.
Corrosion can be prevented by or minimized by one or more of the following method:
- When designing a new system choose corrosion resistant material to minimize the effect
- Apply protective painting
- Protect catholically using sacrifice metals
- Add protective film forming chemical inhibitors.
b). Scaling:
Scale is a dense coating of predominantly inorganic material formed from the precipitation of water soluble constituents
- Some common scales are:
- Calcium carbonate
- Calcium phosphate
- Magnesium salts
- Silica
Four principal factors determine whether or not water is scale formed:
- Temperature
- Alkalinity or Acidity
- Amount of scale forming material present
- Influence of other dissolved materials
Scaling can be controlled by following methods:
- Limit the concentration of scale forming minerals by controlling
- Cycle of concentration
- Feed acid to keep the Calcium carbonate dissolved
- Treat with chemicals designed to prevent scale.
c). Fouling:
It is the accumulation of solid material other than scale in a way that hampers the operation of plant equipment.
Common fouling elements are:
- Dirt and silt
- Sand
- Corrosion products
- Microbial organism
- Aluminum phosphates
See at more here: http://textilelearner.blogspot.in/2013/01/water-treatment-plant-wtp-process.html
