NTPC
Title
:
Ref. No. :
NTPC
STANDARD OPERATING PROCEDURE
Coal mill Inerting operation
OPN/MAIN PLANT/BLR/22
Issue : 1.0
Page 1 of 3
Date :
01-05-2018
PURPOSE: This is used for inerting Operation of Coal mill
SCOPE:It covers Coal mill of Main Plant Lara (2 x 800MW)
RESPONSIBILITY: UCE/Boiler Desk Engineer of concerned unit is responsible for compliance with
this work instruction. The concerned operator executes the work taking all safety precautions as per
the procedure laid down.
Mill Inerting operation:
The purpose of pulverizer inerting is to dilute the oxygen content of the pulverizer when the
risk of a pulverizer explosion is increased, to maintain an inert atmosphere in the pulverizer
with steam, and to extinguish fires in the pulverized fuel system.
Mill Inerting steam Line charging
1. Ensure all mills inerting Block valves and Control Valves are healthy and in closed
condition.
2. Open all 4 inert steam header drains to atm @ 0m. (near Mill E, H, J, B).
3. Open Mill inerting line isolation valve in boiler side (26m).
4. Crack charge the common isolation valve for steam inerting and APH soot blowing in
unit HT PRDS.
5. Ensure dry steam is drained from all the drain valves and line is warmed up.
6. Close the atm drain and fully open the common isolation valve.
7. 15 KSc header pressure & 310 DegC temp to be maintained.
Operation Philosophy




Inerting steam is supplied automatically whenever mill is tripped or mill outlet air
temperature reaches 110°C except Boiler MFT that means all the mills are out of service
simultaneously.
The pressure of steam will be reduced to 0.2 kg/cm2(g) for steam inerting.
the inerting steam at the inlet to pulverizer shall not be exceed 3.0kg/cm2 at any case
like inerting or transportation using control valve(10HHR10AA071) and pressure
transmitter(10HHR10CP101).
The maximum quantity of steam inerting for a mill is approximately 23,400 kg/hr per
mill for transporting mode and 3,600 kg/hr per mill for inerting.
NTPC
Title
NTPC
STANDARD OPERATING PROCEDURE
:
Coal mill Inerting operation
Ref. No. :
OPN/MAIN PLANT/BLR/22
Issue : 1.0
Page 2 of 3
Date :
01-05-2018
Mill Inerting procedure
1.
2.
3.
4.
5.
6.
Close the hot air gate and hot air control damper.
Close the cold air gate and cold air control damper.
Close feeder Outlet gate.
Ensure MDV & BIG is open
Ensure inerting steam line is charged upto MOV from Unit HT PRDS.
Inject steam at a rate sufficient to achieve an inert atmosphere.
Note :
The inert system will be functional at all times except when the pulverizer
discharge valves (10HHE11AA061~10HHE15AA061) are not fully open.(The
steam inerting valve(10HHR10AA071) is interlocked to not open in this case).

The pulverizer can be inerted at any time by manually activating the pulverizer
steam inerting valve (except when the pulverizer discharge valves are not fully
open)
Transporting mode
After resetting the mil trip parameters, operator has to decide whether the unburned coal in
the mill shall be sent to the furnace or to the ground. To send the coal to the furnace by
ensuring the flame, cold air damper shall be opened to meet the minimum cold PA flow(around
95 TPH)
Transporting is conducted manually as follows:
1. Check that all permissive for the mill starting is satisfied.
2. Hot air gate & hot air control damper remain closed.
3. Open Mill Discharge Valves (MDV) and Burner isolation gates (BIG) if they are closed.
4. Open seal air valve and cleaning air valve
5. Close shut-off valve at coal feeder downspout
6. Open steam inerting block valve (10HHR10AA041) if closed
7. Open steam inerting control valve(10HHR10AA071) wide open
8. Open cold air gate & cold air control damper(to min PA flow)
9. Start the mill motor
10. Close the steam inerting control valve after 3 minutes of mill running.
11. Maintain Transportation steam pressure downstream of control valve at 2 kg/cm2.
12. Maintain PA flow(95 TPH) and mill outlet temperature 54°C and continue the mill
running until it is empty.
NTPC
Title
:
Ref. No. :
NTPC
STANDARD OPERATING PROCEDURE
Coal mill Inerting operation
OPN/MAIN PLANT/BLR/22
Page 3 of 3
Issue : 1.0
Date :
01-05-2018
Emptying mode
Emptying is conducted in case of impossibility of using transportation mode. Emptying is
conducted using pyrite removal system. The mode is to remove the accumulated coal in the
mill by rotating scraper.
Emptying is conducted manually as follows:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Check that all permissive for starting the mill motor is satisfied.
Open the pyrite hopper inlet valve if closed
Close Hot & Cold air gate damper
Open seal air valve and cleaning air valve
Close shut-off valve at coal feeder downspout
Open steam inerting block valve if closed
Open steam inerting control valve – inerting position for 30 seconds
Close the steam inerting control valve
Start the mill motor
Prepared by
Checked by
Reviewed by
Approved
Nilakantha Meher
Yousuf Ali
Sr Manager(Oprn)
A.K.Singh
AGM(Oprn)
E.S.Phani Kumar
GM (Oprn)
Asst Manager (Oprn)