Coal power plant

COAL POWER PLANT

In India the major resource for generating electricity is coal. Among all power plants the coal power plant plays a major role. Coal power plants are also named as Thermal power plant or steam power plant. In this power plant, by using coal heat energy of combustion is converted to electrical energy.

*The working principle of coal power plant is based on “Rankin cycle”.

Site selection:

To select the site for installing coal power plant following factors are considered.

1. Supply of fuel: The coal power plant must be place near to the availability of fuel because fuel is the major source to run the coal power plant.

*The most of the coal plant are located at coal mines, due to this reason the cost of fuel is minimum and transportation charges are low.

2. Availability of water:  The coal power plant land mark is provided with huge amount of water. The water is utilized for the purpose of condenser at the time of operating conditions.

3. Transportation facilities: The power plant should well connected to the transportation with other parts of the country by means of road, rail etc… Therefore adequate transportation facilities must exist.

4. Cost and land type:  Whenever the power plant is ready to construct the first step to consider is initializing cost of power plant.

*The initializing cost consists of cheap land, transport facility. After checking all the instants the heavy equipment will launch on a particular selected area.

5. Nearness to load centers:  Load centers are also defined as consumer requirements. If a power plant is placed near the load centers the transportation and electricity transmission charges are low. This concept is applicable only for DC

*In case of AC load centers are away from the power plant due to some important reasons.

6. Away from population: Coal power plant is eco-enemy hence it is preferred installation away from the high density populated areas

-->It is clear that all the above factor`s can`t be favorable at one place. Keeping in a view the fact that now-a-days the supply is form of AC and more importance is given to generation rather than transmission.

Schematic arrangement of steam power station:

 The below diagram exclaims the schematic arrangement of steam power plant. The figure consists of several types of equipments which discussed briefly in below.

Coal storage and Coal handling:

The transported coal from coal mines are send to power plant. The coal is stored in coal storage room, from this room the coal is travel to coal handling plant through convey belts and exculaotrs . This exculators run with the Induction motor.

*In coal handling plant the coal is pulverized with the help of crushers. This pulverized coal is send to boiler. The main purpose of coal storage is to avoid lack of coal at the time of droughts, strikes and environmental conditions etc...

Ash storage and Ash handling:

 The ash is obtained after burning the coal for raising the temperature of the boiler. The obtained ash is send to ash handling plant by means of conveyor the ash is kept in storage and used for many things

 Uses of Ash:

1. Ash is used for construct buildings by making bricks.

2. Ash is used for irrigation purpose, when the irrigation land is in downstream the ash helps to fulfill the area and makes into equal land, after completing this process the layer of red sand is placed over the ash and the red sand is used for irrigation.

  IMPORTANT REQUIREMENTS

1. STEAM GENERATING:

           This part is most important in the entire power station. The steam generating part produces the steam by utilizing water and coal. This part consists of boiler and its furnace, super heater, economizer, air pre-heater.

i) Boiler: A boiler is a closed vessel, by utilizing the heat energy obtained from coal is converted to steam. The boilers are classified into two types:

Water tube boilers	Fire tube boilers
* The name indicates water tube i.e. the water travels through the tube and hot gases flow over the tube.	* In this boilers the hot gases flow through the tubes surrounded by the water.

Among these two, water tube boilers are preferred due to some advantages listed below:

-->Less space required due to smaller size of drums.

-->More working pressure.

-->Less chances to explosion.

ii) Boiler furnace: The boiler furnace is made up of silica, clay, kaolin etc. it is a chamber which produces heat by burning huge amount of coal. It also provides support to the boiler

*These boiler has the properties irrespective to the temperature. The boiler furnace has three types of construction walls.

-->Plain refractory walls – Used for small power plants

-->Hollow refractory walls – Used for large power plants

-->Water walls - Recently developed method used for small and large power plants.

iii) Super heater: Super heater is a device which increases the overall efficiency of the plant by raising the temperature above the boiling point of water.

*A super heater consists of group of tubes made up of special alloy steels such as chromium-molybdenum. These tubes are heated 

when flue gases passes over it. This results in raise in temperature.

*The super heater consists of two types.

Radiant	Convection
*It is placed in between water walls and receives heat from burning fuel.	* It is placed in boiler tube bank and receives heat from flue gases.
Disadvantages: 1. Due to high temperature furnace it may get damaged. 2. If steam output increases, the super heater temperature falls.	Advantages: 1. Steam output increases with increase in temperature of super heater.

*Hence convection type is used rather than Radiant type.

iv) Economizer:  It is a device which heats the fed water on its way to boiler by using the heat of flue gases.

*It consists of large number of closely spaced parallel steel tubes connected by headers. The feed water flows through the tubes and raise the temperature.

*The Advantage of economizer is listed below:

1. Increase in boiler efficiency

2. Fuel saving

3. Reduces stress in boiler due to high temperature feed water.

v) Air pre-heater: The function of air pre-heater is to extract heat from flue gases and give it to the air supplied to furnace. The super heaters and economizers are not exactly extract the heat, hence pre-heater is employed to improve thermal efficiency of plant.

*There are two types of air pre-heater

Recuperative	Regenerative
1. In this type the air pre-heater consists of steel tubes filled with flue gases and heats the air which is passing externally to the tubes.	1. In this type the air pre-heater consists of slowly moving drum made of corrugated metal plates. The flue gases flow one side of drum and air on other side.

2. CONDENSOR:

Condense means cooling. A condenser is a device which condenses the steam at the exhaust turbine.

Functions:

1. It creates a very low pressure based on prime mover. This results in energy condenser

2. The condensed steam can be used as fed water to the boiler.

*The condenser is of two types:

Jet condenser	Surface condenser
In this condenser cooling water and exhausted steam will combined together. As a result there are equal temperatures when leaving from condenser.	In this condenser there is no direct contact between cooling water and steam. The cooling water flows through horizontal tubes enclosed in a cast iron shell and exhausted steam over the surface area. There is a transfer of energy and obtain similar temperature.
Advantages: 1. Low initial cost 2. Less floor area required 3. Less cooling water required 4. Low maintenance charges	Advantages: 1.Condensate can be used as feed water 2.Less pumping power required 3. Creation of better vacuum at Turbine exhausted.
Disadvantages: 1.High power is required for pumping water 2. Condensate is wasted	Disadvantages: 1. High initial cost 2. Requires large floor area 3. High maintenance charges.

3. PRIME MOVERS:

                      Prime mover is a device which converts mechanical energy into electrical energy. The prime mover existed with several advantages listed below:

1. High efficiency

2. Simple construction

3. High speed

4. Low maintenance cost

5. Less area requirement

Requirements of Turbine:

Pelton turbine: Used for high Pressure head

Francis turbine: Used for medium pressure head

Kaplan turbine: Used for low pressure head

4. WATER TREATMENT:

          Boiler is the heart for steam power plant. The plant efficiency depends on boiler. The sea water contains so many salts named hard water which decreases the efficiency to overcome this we may used softened water by removing the hardness. The pure and soft water`s fed to the boiler.

* The cooling towers are used for the gases exhausting and for cooling purpose.

5. ELECTRICAL EQUIPMENT:

   In generating stations there are number of electrical equipments, by using this equipments we can run the power plant

Alternator: The Alternator generates AC voltage which is hydrogen or air cooled.

Transformers:  The transformers used in substations may be step up, step down, general service station on transformer, auxiliary transformer

Switch gears: The substation in built with switch gears consists of circuit breakers, relays, switches and other control devices.

 The below video shows the working of coal power plant

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