Introduction to Coal handling plant
In a coal based thermal power plant, the initial process in the power generation is “Coal Handling”. So in this article i will discuss the overall processes carried out at a Coal Handling plant in a coal based thermal power generating station.
The huge amount of coal is usually supplied through railways. A railway siding line is taken into the power station and the coal is delivered in the storage yard. The coal is unloaded from the point of delivery by means of wagon tippler. It is rack and pinion type. The coal is taken from the unloading site to dead storage by belt conveyors. The belt deliver the coal to 0m level to the pent house and further moves to transfer point 8.
The transfer points are used to transfer coal to the next belt. The belt elevates the coal to breaker house. It consists of a rotary machine, which rotates the coal and separates the light dust from it through the action of gravity and transfer this dust to reject bin house through belt.
The belt further elevates the coal to the transfer point 7 and it reaches the crusher through belt. In the crusher a high-speed 3-phase induction motor is used to crush the coal to a size of 50mm so as to be suitable for milling system. Coal rises from crusher house and reaches the dead storage by passing through transfer point 8.
Equipment used in a coal handling plant
1. Pull chord switch
A series of such switches are arranged in series at a 1m distance on the side of conveyor belt. The power supply to rotor of the conveyor belt is established only if all switches in series are connected.
2. Vibrating feeder
The coal stored in a huge hub is collected on the belt through vibrations created by the vibrating feeder.
3. Flap gates
These are used to channelize the route of coal through another belt in case the former is broken or unhealthy. The flap gates open let the coal pass and if closed stop its movement.
4. Magnetic separator
these are used to separate the ferrous impurities from the coal.
5. Metal detector
The transmitter consists of a high frequency oscillator, which produces a oscillations of 1500 Hz at 15V. The receiver receives this frequency signal. If there is any presence of metal in the coal. Then this frequency is disturbed and a tripping signal is send to relay to stop the conveyor belt.
6. Belt weightier
It is used to keep an account of the tension on the belt carrying coal and is moves accordingly to release tension on the belt.
7. Reclaim hopper
Reclaimation is a process of taking coal from the dead storage for preparation or further feeding to reclaim hoppers. This is accomplished by belt conveyors.
Steam generation from coal
Coal from the coal wagons is unloaded in the coal handling plant. This unloading is done by the “Tipplers”. This coal is transported up to the raw coal bunkers with the help of conveyor belts.
2. Crush House
After hand picking foreign material, coal is transported to the Crush house by conveyor belts where it is crushed to small pieces of about 20 mm diameter. The crushed coal is then transported to the store yard. Coal is transported to bowl mills by coal feeders.
3. Bowl Mill
The coal is pulverized in the bowl mill, where it is grounded to a powder form. The mill consists of a round metallic table on which coal particles fall.
This table is rotated with the help of a motor. There are three large steel rollers, which are spaced 120” apart. When there is no coal, these rollers do not rotate but when the coal is fed to the table it packs up between rollers and the table and this forces the rollers to rotate.
Coal is crushed by the crushing actions between the rollers and rotating tables.
This crushed coal is taken away to the furnace through coal pipes with the help of hot and cold air mixture from P.A Fan. P.A Fan takes atmospheric air, a part of which is sent to Air pre-heaters for heating while a part goes directly to the mill for temperature control.
Atmospheric air from F.D Fan is heated in the air heaters and sent to the furnace as combustion air.
Boiler used in the power plant is suspended type. This prevents it from getting deformed, when a subjected to very high temperatures.
Due to heat and density difference the water rises up in the water wall tubes.
Water is partly converted to steam as it rises up in the furnace. This steam and water mixture is again taken to the boiler drum where the steam is sent to super heaters for superheating.
The super heaters are located inside the furnace and the steam is superheated (540°C) and finally it goes to turbine. Flue gasses from the furnace are extracted by induced draft fan, which maintains balance draft in the furnaces with forced draft fan. These flue gasses emit their heat energy to various super heaters in the pant house and finally pass through air pre-heaters and goes to electrostatic precipitator where the ash particles are extracted. Electrostatic precipitator consists of metal plates, which are electrically charged.
Regular mechanical hammers blows cause the accumulation of ash to fall to the bottom of the precipitator where the bottom of the precipitator where they are collected in a hopper for disposal. This ash is mixed with water to form slurry and is pumped to ash pond.