coal mill & Feedercoal mill & Feeder1 (2).ppt

coal mill & Feedercoal mill & Feeder

1. “MILL, FEEDER INSTRUMENTS &
CONTROL”
RIHAND STAGE-II 2X500 MW
RAJENDRA
PRASAD

2. Components
The Major components are :
•Coal Preparation Equipments
•Mills
•Feeders

3. Why Pulverized Fuel?
The economic motives for the introduction and
development of pulverized fuel firing are:
i) Efficient utilization of cheaper low grade coals.
ii) Flexibility in firing with ability to meet fluctuating
loads.
iii) Elimination of breaking losses.
iv) Better response to automatic control.
v) Ability to use high combustion air temperature;
increasing the overall efficiency of boiler.
vi) High availability.

6. Rollers
Coal Entry
Hot Air
Flow from
PA Fan
Pictures of Bowl Mill

7. Features of Bowl Mills
Grinding chamber
Classifier mounted above it
Pulverization takes place in rotating bowl
Rolls rotating free on journal do the crushing
Heavy springs provide the pressure between the coal and the rolls
Rolls do not touch the grinding rings
Tramp iron and foreign material discharged.

8. Role of Mills
•Produces Pulverized coal 80% of which passes
through 200 mesh
•Air mixed with Pulverized coal (PF) is carried to
the coal nozzle in the wind box assembly.
•PF from coal nozzle is directed towards the centre
of boiler burning zone
•Pre-heated secondary air enters boiler and
surrounds the PF and help in combustion

10. MILL Parameters

11. PULVERISER LOGIC
This logic takes the count of total no. of pulverisers in service at
any point of time,
No. of FD Fans and PA fans in service. With PA Fan ‘ON’ and PA
Header Pressure adequate (>560 mmwcl), it gives “PA permit” to
start the Pulverizer.
In case of PA Header Pressure going low-low or PA/ FD fans
trips, it ensures the shut down of Pulverizers from top elevation to
bottom elevation in a timed sequence.
COAL ELEVATION LOGIC

12. Each mill can be taken in to service manually or automatically.
Auto manual selection push button is available on FSSS console
for each mill. Initially, “Pulverizer Ignition Permit” signal must be
established for the mill to start.
Other condition required to be established for starting the mill are
as follows:-

13. IGNITION PERMIT FOR MILL
PRIOR TO START ANY MILL THE MILL IGNITION ENERGY
MUST BE ADEQUATE TO SUPPORT COAL FIRING
IGNITION PERMIT FOR MILL –A
MINIMUM 3 OUT OF 4 HONVs OF ELEV. AB OPEN
OR
MILL-B IN SERVICE WITH >50% LOADING AND BOILER
LOAD IS > 30%

14. IGNITION PERMIT FOR MILL –B
MINIMUM 3 OUT OF 4 HONVs OF ELEV. AB OPEN
OR
MILL-‘A’ OR “C” IN SERVICE WITH>50%
LOADING AND BOILER LOAD IS > 30%

15. IGNITION PERMIT FOR MILL –C
MINIMUM 3 OUT OF 4 HONVs OF ELEV. CD OPEN
OR
MILL-‘B’ OR “D” IN SERVICE WITH>50% LOADING
AND BOILER LOAD IS > 30%
OR
MINIMUM 3 OUT OF 4 HONVs OF ELEV. AB OPEN AND
MILL-B IN SERVICE WITH >50% LOADING AND BOILER
LOAD IS >30%


16. IGNITION PERMIT FOR MILL –D
MINIMUM 3 OUT OF 4 HONVs OF ELEV. CD OPEN
OR
MILL-‘C’ OR “E” IN SERVICE WITH>50% LOADING
AND BOILER LOAD IS > 30%


17. IT IS USED FOR PROVIDING PATH FOR P.A. TO
INDIVIDUAL MILL.
It consists OF –
SOLENOID
POWER CYLINDER
LIMIT SWITCHES
HOT AIR GATE (HAG)

18. FOR OPEN HAG---
OPEN PB PRESSED & MILL ON & HAG NOT
OPEN
FOR CLOSE HAG---
CLOSE PB PRESSED & HAG NOT CLOSED
OR
MILL OFF & HAG NOT CLOSED
OR
LOSS OF DC > 2 Sec. & HAG NOT CLOSED
HOT AIR GATE (HAG)

19. HOT AIR GATE (HAG)
HAG CLOSE CONDITIONS
MILL O/L TEMP. HIGH & HAG NOT CLOSED
AUTO STOP & HAG NOT CLOSED
UNSUCCESSFUL START & HAG NOT CLOSED

20. COAL MILL PERMISSIVES & PROTECTIONS
COAL MILL PERMISSIVES & PROTECTIONS

21. Gravimetric Feeder

22. FEEDER INSTRUMENTS
•LOAD CELL
•CMMR
•COAL ON BELT
•DISCHARGE PLIGEGE
•EDDY CURRENT CLUTCH
•SHEAR PIN (COC)

23. Feeder start Logic
Feeder start command is given from FSSS Elevation
Logic only.
This command is continuously required to keep the feeder
in service.
Feeder speed demand minimum, Pulverizer ON,
pulverizer outlet temp > 130OF, HAG open and no MFT
are the important conditions required to give the feeder
start command from FSSS.

24. FEEDER START LOGIC
In case of pulveriser power high, bowl DP High or feeder
OFF command, feeder speed demand is driven to minimum.
Release feeder to Auto Signal is also coming from FSSS. All
of the above conditions are present and feeder is not ON for
more than 50 seconds, release signal for auto is available

26. THANK YOU …
QUESTIONS ?