COAL HANDLING PROCESS IN NTPC FARAKKA THERMAL POWER PLANT

COAL-HANDLING process

From the track hopper 200mm coal is transferred to the conveyor via paddle feeder and finally sent to the crusher house.

               In the Crusher House the vibrating screen sends the coal having size of less than 20mm to belt feeder through the bypass chute bypassing the crusher and sends the coal of more than 20mm size to the crusher. 

                                               PICTURES ABOVE ARE OF COAL CRUSHERS

VIBRATING SCREEN

COAL MILL

 Mill is used to pulverize the coarse coal into fine powder and transport the same to furnace with the help of PA fan.

Ø  Because of pulverization following advantages are drawn.

1. Better Air - Coal fuel ratio.

2. Better flame stability

3. Effective utilization of carbon.

4. Efficient use of low grade coal in Boiler.

5. Reliable, safe and flexible operation.

6. All the above will increase the efficiency of the boiler

v GRINDING PROCESS OF MILLS.                                    

·       Coal are fed from raw coal feeder (situated just above the mill on concrete floor). One end of the raw coal feeder is attached with Coal bunker through a coal gate.

·        Raw coal feeder is having a travelling belt with coal weighing instruments. Coal from travelling belt of raw coal feeder drops in central feed pipe (connection between Raw Coal Feeder and Mill).

·       After coal reaches Mill bowl grinding started and hot air also been given to make the pulverized fuel dried enough to classifier chamber. The portion of the coal which cannot be grinded finds its way to mill reject.

·       Mechanical setting is to be carried out for minimum rejects. Zero rejects also is not good as it causes excessive wear and tear of the mills.

·       Once the fuel air mixture reaches classifier it will again classified into two parts one part which heavier part will go back to mill for further grinding other part will directly go to furnace through four coal pipes and MDV (Mill discharge valves).

COAL MILL 

v COAL VARIATION IN INDIA

ü  Moisture 5 to 30 %

ü  Ash 10 to 55%

ü  Volatile matters 12 to 40%

ü  Abrasion Index mg/kg 60 to 125

ü  Hard Groove Index(HGI) 45 to 110

v EFFECTS OF COAL ELEMENT ON MILL CHOICE AND SIZING

·       MOISTURE - More hot air is required to dry the coal particles.

·       VOLATILE MATTERS- Determine temperature of Mill outlet and furnace.

·       ASH - Grinding element; coating on rollers etc.

·       HGI - Grind ability

v NOMENCLATURE OF BOWL MILLS

v FOR XRP xxxx ( e.g. 803 /883)

ü  X stands for Frequency of Power Supply (50 Hz for India)

ü  R stands for Raymond (inventor of Bowl Mill)

ü  P stands for Pressurized Mill with Primary Air Fan

ü  100/110 stands for Bowl diameter (inches) (in case of xrp1003 /xrp 1103)

ü  3 stands for Number of grinding Roller.

v STANDARD MILL CAPACITY

         In NTPC Farakka XRP 803 and XRP 883 bowl

v MILL SIZE CAPACITY (COAL GRINDING)

ü  XRP 623 18 + TPH

ü  XRP 703 26 + TPH

ü  XRP 763 33.8 TPH

ü  XRP 783 36.5 TPH

ü  XRP 803 39.8 TPH

ü  XRP 883 51 + TPH

ü  XRP 903 54+ TPH

ü  XRP 1003 68 .1 TPH

ü  XRP 1103 HP 91 + TPH