COAL BASED THERMAL COAL BASED THERMAL POWER PLANTPOWER PLANT

A thermal power station is a power plant in which the prime mover is

steam driven. Water when heated turns into steam which drives a steam

turbine.

After passing through the turbine, the steam is condensed in a condenser

and recycled to where it was heated. [Rankine cycle]

Coal is used as a fuel to heat water in a coal based thermal power

plant.

Thermal Power PlantThermal Power Plant

Installed Capacity (October 2010)Installed Capacity (October 2010)

Stage 1: Conversion of Chemical energy of coal to heat energy in boiler.

Stage 2: Conversion of heat energy to mechanical energy of steam.

Stage 3: Conversion of mechanical energy to rotational energy of turbine which drives generator.

Stage 4: Rotational energy to electrical energy based on Faraday’s Law of electromagnetic induction.

Energy ConversionsEnergy Conversions

Energy ConversionsEnergy Conversions

Modified Rankine CycleModified Rankine Cycle

1. Coal Handling Plant

2. Boiler and its auxiliaries

3. Turbine and its auxiliaries

4. Condenser and Cooling Tower

5. Ash Handling Plant

6. Electrical Equipments

Major Components of Coal Based Thermal Power Plants

Major Components of Coal Based Thermal Power Plants

Steam Flow DiagramSteam Flow Diagram

Coal to ElectricityCoal to Electricity

• A coal handling plant is the area of the thermal power plant where the raw coal is brought from the coal mines and is processed into a form that can fed into the boiler.

1. Transportation System

2. Coal Crusher

3. Coal Storage Area

4. Pulverizer

5. Conveyers

Coal Handling SystemCoal Handling System

The transportation system is the various methods through which the raw coal is brought into the plant

The usual system is through trains but many other methods are followed . some of the methods are as follows :

Merry go round: in this in spite of following the conventional method of trumpling the railway wagon upside down the wagons are provided with a door at the bottom from which the wagons are emptied on an under ground conveyor belt which take the coal to the

crusher house .

Transportation System

Other methods for coal transportation are as follows:

• Transportation through ships is done when the power plant is situated near the sea area.

• When the power plant is situated near the coal mine the coal is directly fed into the plant through conveyers.

• Some times road transportation is used cut in very rare cases because it is unable to supply the amount needed for undisturbed power generation.

• Sometimes the coal is also transported by pipelines. This is method is said to be more efficient as it is not affected by the traffic and weather conditions

Transportation System

• Once the coal is in plant it has to undergo some preparatory processes before being fed into the boiler

• First the coal goes to the crusher house where the coal is crushed manually into a size of about 20mm .This coal is then passed further some part of it is fed into the plant while the other is stored.

• Generally most of the power plants store a coal for the use of 20 days this is known as dead storage.

Coal Processing

• The coal is then is passed through vibrator which separates the 20 mm sized coal from larger one. This 20 mm coal is then fed into the raw coal bunker from where it goes to the coal mill .The rate of feeding of coal is controlled by raw coal feeder.

• The coal mill pulverizes the coal i.e. it crushes the coal into a tiny sized particles which are similar to that of talcum powder. It is done to avoid incomplete combustion of

Coal Processing

Boiler

• Boiler is a container into which water can be fed and steam can be taken out at desired pressure, temperature and flow

Construction

• It is rectangular in cross section and wall made of tubes hence all four walls are made of tubes which contain water

Firing in boiler

• Corner fired boilers are used now days and in these all nozzles face downwards and burning takes place in the coal firing wall called fire wall

Economiser

• Economiser is there to improve the efficiency of boiler by extracting heat from flue gases to heat water and send it to boiler drum.

Advantages of Economiser

Advantages of Economiser include• Fuel economy: - used to save fuel and increase

overall efficiency of boiler plant.• Reducing size of boiler: - as the feed water is

preheated in the economiser and enter boiler tube at elevated temperature. The heat transfer area required for evaporation reduced considerably.

Air Preheater

• The heat carried out with the flue gases coming out of economiser are further utilized for preheating the air before supplying to the combustion chamber

Reheater

• Raising the temperature of steam after part of the energy is extracted from it in the steam turbine called re-heating of steam which increases the cycle efficiency.

• This reheating is done in the boiler, which supplies super heated steam to the turbine itself at the heating surfaces called Reheaters

Steam turbines

• Steam turbine is used as a prime mover• It is a 3 cylinder turbine• HPT• IPT• LPT

Condensers• Condensers are heat exchangers which convert steam from

its gaseous to its liquid state at a pressure below atmospheric pressure (0.91Kg/cm2).

• Two types: i) Air Cooled ii) Water Cooled• Convert the turbine exhaust steam into pure water so that it

may be reused in the steam generator or boiler as boiler feed water.

Boiler Feed Pump

• It is a pressure raising device.• Pumps feed water to Economiser.

• BFP is the biggest auxiliary equipment after Boiler and Turbine.• It consumes about 4 to 5 % of total Electricity Generation.• NPSH avoids formation of water vapour in the Impeller.

Booster Pump

Motor6.6Kv

1500rpm

Hydraulic Coupling

Pump(6 - Stage)

10-4500rpm

NPSH

Deairator

Cooling Tower

• It is a heat rejection device.• A small portion of the water being cooled is being

evaporate into a moving air stream to provide significant cooling to the rest of that water stream.

• For 200MW plant 600m3/hr water is evaporated.• Categorization by air-to-water flow– Crossflow– Counterflow

Types of Cooling Towers

• Natural Draft Cooling Tower: which utilizes buoyancy via a tall chimney.

• Mechanized Draft Cooling Tower: which uses power driven fan motors to force or draw air through the tower.

Types of Mechanized Draft Systems

• Forced draft system: A mechanical draft tower with a blower type fan at the intake.

• Induced draft system: A mechanical draft tower with a fan at the discharge which pulls air through tower.

• Balanced draft system: In this system both FD fan and ID fan are provided.

Ash Handling System• Ash handling refers to the

method of collection, conveying, interim storage and load out of various types of ash residue left over from coal combustion processes.

• Indian coal has high content of ash. Out of which: – 20% is Bottom Ash– 80% is Fly Ash.

Types of Ash Handling

• Bottom Ash - At the bottom of the furnace, there is a hopper for collection of bottom ash. This hopper is always filled with water to quench the ash and clinkers falling down from the furnace. This ash is then passed through Clinker Grinder or Scrapper convertor.

• Fly ash - is captured and removed from the flue gas by ESP or fabric bag filters located at the outlet of the furnace and before the ID fan.

• Fly Ash Handling is done as:a)Dry Fly Ash Handling: i)Evacuated ii)Pressurizedb) Wet Fly Ash Handling

Generator

• Rotor

• Stator

• Excitation System

• Cooling System

Advantages of Coal Based Power Plant

• They can respond to rapidly changing loads without difficulty

• A portion of the steam generated can be used as a process steam in different industries

• Steam engines and turbines can work under 25 % of overload continuously

• Fuel used is cheaper• Cheaper in production cost in comparison with that

of diesel power stations.

Disadvantages of Coal Based Power Plant

• Maintenance and operating costs are high• Long time required for erection and putting into

action• A large quantity of water is required• Great difficulty experienced in coal handling• Presence of troubles due to smoke and heat in

the plant• Unavailability of good quality coal• Maximum of heat energy lost• Problem of ash removing.

SUPERCRITICAL TECHNOLOGY

• Supercritical steam parameters results in higher efficiencies – above 45%.

• The supercritical coal based units have faster starting time and load changes and are more suitable for daily start up/shut down operation.

Block Diagram of Super Critical Technology

Advantages of Supercritical Technology

• Reduced fuel costs due to improved plant efficiency• Significant reduction in CO2 emissions• Much reduced NOx, SOx and particulate emissions• Excellent availability, comparable with that of an

existing sub-critical plant• Plant costs comparable with sub-critical technology

and less than other clean coal technologies• Compatible with biomass co-firing• Can be fully integrated with appropriate CO2 capture

technology

Ultra Mega Power Projects (UMPPs)

• Development of Ultra Mega Power Projects (UMPPs) has been identified as a thrust area. These are very large sized projects, approximately 4000 MW each involving an estimated investment of about Rs. 16,000 crore .

• Ultra Mega Power Projects would use Super Critical technology with a view to achieve higher levels of fuel efficiency, which results in saving of fuel and lower green-house gas emissions.

Ultra Mega Power Projects(cont..)

• These projects will meet the power needs of a number of States/ distribution companies located in these States, and are being developed on a Build, Own, and Operate (BOO) basis

• Flexibility in unit size subject to adoption of specified minimum Supercritical parameters

• Integrated power project with dedicated captive coal blocks for pithead projects

• Coastal projects to use imported coal

Mixing Solar with Coal to Cut Costs

• A new strategy that could reduce coal plant emissions and cut the cost of solar power.

• In the new project, because parabolic troughs don't generate sufficiently high temperatures, the heat they produce won't be fed directly into the turbines.

• Instead, it will be used to preheat water that will be fed into the coal plant's boilers, where coal is burned to turn the water into steam.

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