Coal and their Types

Coal acts as a main fuel used for the generation of power in the thermal power plant. In many Power plants, with the help of the fossil fuel the plants are operated. The maximum requirement of the fuel in the thermal power plants is coal.

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Types of coal:

  • Peat
  • Bituminous
  • Semi bituminous
  • Lignite
  • Anthracite

Analysis of coal:

The analysis consists of two types they are

  • Proximate Analysis
  • Ultimate Analysis
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Proximate Analysis

The proximate analysis is used to determine the fixed amount of the carbon, moisture, volatile matters and ash present in the sample of the carbon.

S.No Constituents percentage
1 Fixed carbon 16-92
2 Moisture 3-30
3 Volatile Matter 3-50
4 Ash 2-30

Ultimate Analysis

The ultimate analysis is used to determine the component of coal in the form of the chemical elements.

S.No Constituents percentage
1 Sulphur 0.5 – 3
2 Nitrogen 0.5 – 7
3 Hydrogen 1 – 5.5
4 Ash 2 – 40
5 Carbon 50 – 95
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Coal Handling

To handle the fuel like coal, each and every station of the power plant is furnished with the coal handling equipment. Coal is transferred with the help of the handling equipment, which is the initial process of the power generation. The maintenance of the coal handling plant in the thermal power plant is typical. Failure of the equipment leads to the high operation cost and also maintenance cost.

Parts

Coal conveyor: It is used to send or transfer the coal with the help of the belt conveyors with high efficiency.

Coal conveyor

Pulverizer: The combustion efficiency of the coal is increased by using the Pulverizer

Pulverizer

Boiler: Heat energy must be applied to water to develop a steam

boiler-plant

Superheater: By using the steam engine it converts the wet or saturated steam into the dry steam. It sends the dry steam into the furnace with the help of the pipes, which is known as the super heater.

Superheater

Economizer: The economizer is used to perform the operation like pre-heating a fluid.

Economizer

Re-heater: In the high pressure system heat is added by the re-heater

Re-heater

Steam turbine: It is a mechanical device. Thermal energy is extracted by the pressurized steam. The created energy must be converted into the rotary motion.

Steam turbine

Generator:  Generator is a device used to convert the mechanical energy into the electrical energy

Condenser: Condenser is used for cooling and it converts the gases substance into the liquid substance.

Deaerator: It is used to remove the air and gases from the feed water to steam generating boiler.

coal-1
Functioning of the system:

  • By using the conveyors the coal is transfer to the coal bunkers. Then the raw coal must be cut into the pieces nearly of 5cm in size.
  • The small pieces of the coal can be made to burn easily and completely.
  • With the help of the mill grinders the coal pieces are converted into fine power and the power must be mixed with the combustion air. The mixture must be transfer to the furnace. Pre-heat treatment is provided to the coal to eliminate the excess moisture content from the coal.
  • The efficiency of the coal is increased by applying the pulverizing operation. So, the pulverized coal must be producing the steam. After completion of the pre-heating, water from the feed pump are made to enter into the boiler.
  • The water sent to the condenser can be reused. This is done by using various application and process. The vaporized and heated fluids must be set off from the boiler.
  • In the boiler the steam is produced and the produced steam must be sent into the steam drum.
  • When it reaches the saturation temperature it is send to the super heaters.
  • It turns the steam into energy source and it rotates the turbine.
  • The flue gases carry out a lot of heat from the boiler. So the economizer extracts the heat from the flue gases and then is used for the heating the feed water. It results in the saving the coal consumption and gives high boiler efficiency.
  • The re-heater acts as a steam boiler, where the heat is added to the high pressure steam. Here, the energy must be transfer to the pressure turbine.
  • After re-heating of the steam it is used to rotate the steam turbine, where the heat is converted to the mechanical energy.
  • The developed mechanical energy must be used to run the generator which is fixed to the turbine, there by producing the electrical energy.
  • Series of steam turbines are interconnected to each other in the turbine generator.
  • Throughout the system the steam is made to move, where it releases the pressure and the thermal energy, plus the volume is made to expand.
  • After rotating the steam turbine the steam comes into the condenser.
  • The condenser is used to condense the outlet steam from the steam turbine.
  • The condense steam must be in the form of pure water
  • Then the water must be pumped back to the boiler.
  • The boiler feed water must be utilized by the steam generating boiler and it should be lacking of air and dissolved gases mostly corrosive once.
  • To avoid the corrosion deaerator is used in the power station. It removes the air and dissolved gases from the boiler feed water.
  • On the horizontal cylinder the desecration section is arranged, which acts as a storage tank.
  • The pressure steam is used to push the turbine blade which helps to turn the turbine shaft. To the generator shaft the turbine shaft is connected, to the magnet spin within the coils to produce electricity.
  • Through the power grid lines the electricity which is sent to reach the locations.

Cold storage:

Storage of coal is disagreeable because the cost is more and also some more factors are involved

  • Spontaneous combustion of the coal takes place
  • Possibility of damage and corrosion during storage
  • Capital cost of the coal is high

Coal storage types:

  • Dead storage
  • Live storage

Dead storage

Due to the failure of the coal supply for the regular, at that instance the stored coal is supplied. For the long term storage, the coal requires protection spontaneous combustion and weathering.

Live storage

For day to day usage it delivers the coal to the plant. Capacity of the storage is less when compare to the dead storage. They are stored in the vertical cylinder bunker. Usually bunkers are diamond shaped. They are made up of reinforced concrete or steel

Coal transportation takes place with the help of the following

Ways:

  • Rail ways
  • Road ways
  • Rope ways
  • Water ways
  • Airways

Railways

Railways are the cheap and provides best facility at entrance way

Roadways

At the time of transport the common man fears about the thefts

Ropeways:

The ropeway facilities are available near to the coal mines

Waterways

The waterway transportation is difficult, as there is a possibility of coal dips in water.

Airways:

The airways are available near to the runway which are quit an expensive mode to transport the coal.

Finally as to compare to all the transport methods, the power plant stations are mostly preferred to be near to the railways. The railway lines are taken in to the power plant station. The coal must deliver in to the storage room or yard.

Equipment used in the coal handling Plants:

  • Pull Chord Switch
  • Vibrating feeder
  • Flap Gates
  • Magnetic separators
  • Metal detectors
  • Belt Weightier
  • Hopper

Pull Chord Switch

In the coal handling power plant, a series of switches are arranged with a distance of 1m on the conveyor-belt. The switches are connected in series format; the power supply to the rotor of the belt or to the conveyor is supplied.

Vibrating feeder

The vibrating feeder creates a vibration to collect the coal through the belt from the yard or huge hub.

Flap Gates

The flap gates are used to provide way to coal through the belt. In that case, if the gates are open then the coal passes, or if they are closed then the movement must be stopped.

Magnetic separators

The magnetic separators are used to separate the impurities from the coal like ferrous etc.

Metal detectors

The metal detectors are used to detect the impure metal like ferrous and non-ferrous metals and they send a signal to dispatch the metal from the system. The system consists of receiver and transmitter. The receiver is used to receive the signal, and to remove the detected metal plus to stop the conveyor belt. The transmitter is used to produce an oscillation of nearly 1500HZ to 15 Volts.

Belt Weightier

The belt weightier is used to release the tension of coal carrying belt.

Reclaim Hopper

By using the belt conveyors the coal is taken from the storage to the power plant for preparation.

Conveyor system present in the power plant

  • Belt conveyors
  • Vibrating feeders
  • Idlers
  • Pulleys
  • Wagon tipplers
  • Coal Crushers

Belt conveyors

Belt conveyors are used to transfer the material from the storage for the process of the power plantation. By using the belt conveyors it transfer the material continuously. The belt works with the help of frictional force.

 coal-2

The belt conveyors are simple in structure and also easy to maintain. It transfers the material to the long distance with high capacity. The belt conveyors are used in the coal industry, mining industry, and metallurgical industry to transfer the materials from one place to other. It transfers the material at the temperature of lower 50 and it ranges from -20 to +40. The belt conveyors maintain an average speed of 60 – 100 m/min, and the capacity is 50 – 100 tones/hr. It travels a maximum distance of 400m.

Advantages:

Power consumption is low

Maintenance cost is low

Capacity is high

Coal transfer rate must be changes rapidly

Disadvantages:

It is not suitable for shorter distance

It is restricted for slurry and dust particles.

Vibrating Feeder:

The vibrating feeder is used to transfer the material in large size in the production flow. By using the vibrating feeders we can vibrate the material for moving. The feeder consists of magnitude and vibration. The magnitude is used to know the direction, down or side. Smaller objects are used to transfer the material. By varying the speeds the flow rate of the material must be measured by using the belt weigher, and by varying the speed of the belt conveyor the flow rate must be control.

Idlers

The idler consists of three rollers which are fitted to the bearings. To increase the life of the belt the profile makes like an arc and also avoids sharp bends. The fitting arrangements are available in two types they are fixed fitting and detachable fitting.

Pulleys

The pulleys are made up of cast iron. To reduce the belt stress pulley diameter is en-large. The width of the pulley must be 150mm and more than the belts.

Wagon tipplers

It consists of a gear boxes and motor assembly. Within a less amount of time the wagon tipplers unloaded the coal into a hopper.

Coal Crushers

Churches are used to make the coal to form a required shape.

Operational cycles:

  • Normal Bunkering cycle
  • Stacking cycle
  • Reclaiming cycle

Normal Bunkering cycle:

By using the coal wagons the coal is directly shifted from the yard to the coal bunkers, which is known as the normal bunkering cycle.

Stacking Cycle:

When there is no requirement of the coal at the bunkers, at that condition they unloaded the received coal at the yards.

Reclaiming cycle:

When the coal wagons are not available and there is requirement of the coal in the bunkers, at that stage the bunkers are filled by the stacked coal, which is known as the reclaiming cycle.

Problems faced in the coal handling plant:

Design problem

Rainy season Problem

Miscellaneous problems

Advantages:

  • Coal must be easily combustible and even burns at the low temperatures
  • When compare to the other boilers manufacturing of coil fired boilers are cheaper and simpler
  • They are distributed throughout the world
  • By using this we can generate large amount of electricity

Disadvantages:

  • Density of the coal is low and it produces a least energy with tons of fuel
  • Transportation cost of the coal is high
  • Coal dust is very harmful and it releases very harmful gases
  • Storage cost of the coal is considered to be high

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