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WTP p ro ce ss

Water Treatment Plant (WTP) | Process Sequence of WaterTreatment Plant

Water Treatment Plant:The water available f rom dif f erent water sources cannot be used directly in boilers as such. The objectiveof water treatment plant is to produce the boiler f eed water so that there shall be:

1. No scale f ormation

2. No corrosion

3. No f ouling

The treated water is called ‘De-mineralized Water ’ and the plant where it is treated is called WaterTreatment Plant. Process Sequence of Water TreatmentPlant

Water f rom river ↓ Flash mixer ↓ Clarif ier ↓ Filter pack ↓ Clarif ied water tank ↓ Softening plant ↓ Sof t water to various units

Step Discussions:

Water from river: Water comes f rom various rivers in watertreatment plant.

Flash mixer: In this segment Al2 (SO4)3, polymer etcare mixed in water.

Softening plant: In this segment activated carbon are usedas a sof tener.

Soft water to various units: Af ter sof tening of water it is supplied in various units f or various purposes.

There are two types of water are prepared in water treatment plant:

1. Clarif ied water f or washing purpose.

2. Sof t water f or dyeing purpose.

Chemicals are Used in WTP:

1. Aluminum Sulphate

2. Polyelectrolyte

3. Sodium Chloride

Amount of Chemical Used:

1. Polymer- .1% solution

2. Al2 (SO4)3- 10% solution

3. Lime- 10% solution

Experiments Performed in WTP:

1. Total hardness test

2. Jar test

3. pH meter test

4. Titration f or chlorine content test

Requirements of WTP: The importance of maintaining supply of high purity water f or Boiler purposes in Thermal power stations iswell recognized. The presence of undesirable contaminants in water exceeding the f ew PPB level may leadto serious consequences.

The requirements of pure water have been met by recent developments of improved ion exchange resinsand regeneration techniques.

The need f or removal of dissolved solids f rom water arises under several situations. These range f romef f luent water treatment, water purif ication f or portability, treatment as boiler f eed and other industrialapplications.

Why Water Treatment is Required? If proper treatment is not done f or water then Corrosion, Scaling, Microbiological contaminants and f oulingwill 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 commonlyused 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 f ollowing method:

1. When designing a new system choose corrosion resistant material to minimize the ef f ect

2. Apply protective painting

3. Protect catholically using sacrif ice metals

4. Add protective f ilm f orming chemical inhibitors.

b). Scaling: Scale is a dense coating of predominantly inorganic material f ormed f rom the precipitation of water solubleconstituents

Some common scales are:

Calcium carbonate

Calcium phosphate

Magnesium salts

Silica

Four principal f actors determine whether or not water is scale f ormed:

1. Temperature

2. Alkalinity or Acidity

3. Amount of scale f orming material present

4. Inf luence of other dissolved materials

Scaling can be controlled by f ollowing methods:

Limit the concentration of scale f orming 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 plantequipment.

Common f ouling elements are:

1. Dirt and silt

2. Sand

3. Corrosion products

4. Microbial organism

5. Aluminum phosphates

Process in Water Treatment Plant: The treatment process can be divided in two sections:

1. Pre treatment methods

2. Demineralization methods

Pre-treatment Methods: Pre-treatment plant removes suspended solids like clay, salt, plants, micro-organisms, etc. f orm raw waterto give clarif ied water. Suspended solids can be separable or nonseparable.

Separable solids are heavier & large and can easily be removed by an aerator. Non-separable solids havef iner size and taken long to settle down. Hence they are required to be f locculated.

In this, water is f irst dozed with lime and alum. This f orces f iner particles to coagulated increasing theirweight and size. Non-separable solids can now be separated in clarif locculator. The clarif ied water is thenstored in clarif ied water storage tanks.

Following are the dif f erent pre-treatment methods used in water treatment plant:

1. Mechanical methods

2. Chemical methods

Demineralization Methods: The f ollowing methods are normally used f or demineralization of water:

1. Membrane based physical process and electro chemical process

2. Separation by Phase change method

3. Ion exchange method

Factors for Selection of Treatment Methods: The f ollowing specif ic site f actors are to be considered in choosing the treatment method:

Feed water source and quality available

Feed water cost and quantity available

Final makeup water quantity and quality required

Final make up water maximum and average f low required

Chemical storage handling and usage cost

Waste disposal cost and waste treatment equipment available

Existing water and waste treatment equipment available

Operation & Maintenance cost

Storage capacity

Other Factors to be Considered:

Short or long term requirement of equipment or service

Acceptable limitations on membrane liability

Operating labour availability

Capital available

Environmental policy

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