Coal handling system in thermal power plants

Coal handling system in thermal power plants

Thermal power plants require large amount of coal per day. A 100 Mw plant require 1200 ton coal per day.

Selection of coal for power plants-

The coal for thermal power plant should have following properties:

   1)    It should have high heating value.

   2)    It should have less sulphur content.

   3)    It should have low ash content.

   4)    It should have high weatherability.

   5)    It should burn freely to complete combustion.

The various steps involved in coal handling system are as follows:

fig.Coal handling system in thermal power plants

   1)    Coal delivery- Coal from mines is transported by trucks, rail or by ships. If the distance between coal mine and plant is less than 10 km then rope ways are used to transfer the coal.

   2)    Unloading of coal- Unloading of coal is depends on the mode of transport use for coal delivery. 

     When coal is delivered by trucks there is no need of unloading equipments as truck dump coal directly. 

     When coal is delivered by rail then car shakes and rotary car dumpers are used for unloading.

     When coal is delivered by ships then coal accelerators, portable conveyors, self unloading boats, unloading bridges and coal towers are used for unloading of coal.

   3)    Preparation of coal- The coal received from mines is of different sizes which cannot be directly fed into the furnace. For effective burning of coal ,it is crushed by passing through crushers. Crushed coal passed through sizer to remove bigger size coal.

   4)    Transfer of coal-The coal after the preparation phase it is transfer to the storage. The coal is transferred with the help of

      a)     Belt conveyors

      b)    Screw conveyors

      c)     Bucket elevators

      d)    Grab bucket elevator

      e)     Flight conveyors

   5)    Outdoor storage- In outdoor storage, coal is store for 30 to 80 days as balance coal if there is any delay in the transportation of coal to plant. Outdoor storage is provided to avoid shutdown of plant.

   6)    Covered storage- In covered storage, coal is store to supply directly to furnace. It is also called live storage or active storage as it provides coal directly to furnace.

   7)    Inplant handling- In inplant handling, coal is transferred from live storage to feed into the furnace. The coal is transferred using belt conveyors or by screw conveyors.

   8)    Weighing of coal- Before feeding coal to the furnace it is weighted using various methods. 
     There are main three methods are used for weight
     a)     Mechanical
     b)    Pneumatic
     c)     Electronic
      

   Usually movable weigh lorry is used for weighing of coal and after weighing it placed infront of the boiler furnace.

   9)    Furnace firing-As per the requirement, coal is fed to the furnace for burning.

Requirement of good coal handling plant-

   1)    It should be simple and reliable.

   2)    It should have low maintenance.

   3)    It should supply coal continuously as per requirement.

   4)    Cost of coal handling should be minimum.