Sadc Lecture

7/31/2019 Sadc Lecture

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23 May 2012 PMI Revision 00 1

SADC(SECONDARY AIR DAMPER CONTROL)


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SADC STANDS FOR

SECONDARY AIR DAMPER CONTROL

It consists of a number of dampers located atvarious elevations of fuel compartments anddampers in between the fuel compartments. Thesedampers are required to modulate as a function of

certain process variables.


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SADC is divided into two main classifications depending onthe type of modulation they are required to perform.

Fuel Air Dampers : Modulated in proportion to the rate of

fuel fired in that elevation. Auxiliary Dampers: group-controlled in proportion to the

wind box furnace differential pressure.

Auxiliary air dampers are modulated to maintain a fixed

differential pressure between the wind box and the furnace,whereas the fuel air dampers are modulated in proportion tothe rate of fuel fired in that elevation.


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COAL AIR DAMPERS:

A, B, C, D, E, F, G, H, J, K.

OIL AIR DAMPERS :

AB, CD, EF, GH, JK.

AUX. AIR DAMPERS:

AA,BC,DE,FG,HJ,KK.

OVERFIRE DAMPERS:

OFA(U), OFA(L).



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EACH DAMPER IS EQUIPPED WITH A PNEUMATIC

POWER CYLINDER SUITABLE FOR 0.2 TO 1 KSCSIGNAL INPUT.

1-FOR 1 KSC SIGNAL INPUT -----AIR DAMPER TO CLOSE.

2-FOR 0.2 KSC SIGNAL INPUT ----AIR DAMPER TO OPEN.

3- LOSS OF SIGNAL ---------------- DAMPER TO OPEN.

* THE BOTTOM ELEVATION OF S.A.D IS EXCLUDEDFROM ALL CONTROL SYSTEM EXCEPT FOR OPENPOSITION TO ID FAN START SEQUENCE ANDINTERLOCKS.


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SAD CONTROL WHEN BOILER LOAD< 3O% BLI, ALL SAD CONTROL UNITS WILL

BE ON AUTOMATIC CONTROL (i.e. ON LOGIC OVERRIDE) TOMAINTAIN THE DESIRED D.P. BETWEEN WIND BOX TOFURNACE.

WHEN BOILER LOAD REACHES 30% OF BLI THE BMS LOGIC WILLCOMMAND CLOSE THE DAMPER (SAD) WHICH DOES NOT HAVEAN ASSOCIATE MILL IN SERVICE .FROM 10 SEC INTERVAL BMSLOGIC CLOSE THE SAD, STARTING FROM TOP ELEVATION TOBOTTOM ELEVATION.

OIL BURNER DAMPER:WHEN OIL GUN IS IN SERVICE, ITS DAMPER IS FULL OPEN.AFTERREMOVING OIL GUN, THE DAMPER OPENING IS SYNCHRONIZEDWITH OTHER SEC. AIR DAMPER POSITION.



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COAL AIR DAMPERS: THEY ARE OPERATED AS PERAUTO DEMAND FROM FEEDER SPEED.

AUX. AIR DAMPERS: THEY ARE OPERATED IN ORDERTO MAINTAIN WINDBOX TO FURNACE DP TO100MMWCL.

OIL AIR DAMPERS: WHEN OIL GUN IS IN SERVICE,THEY ARE OPENED TO 30%, ELSE THEY WILL TAKETHE DEMAND OF AUX. AIR DAMPERS, WHEN OIL IS

NOT IN SERVICE.

OFU / OFL: THEY ARE OPERATED IN ORDER TOCONTROL SOX/NOX EMISSION FROM THE FURNACE,WHEN TOP MILL IS IN SERVICE.



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SYMBOLS


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There are 88 nos. of pneumatic actuators installedin Secondary Air Damper Control (SADC) systemof each 500 MW unit which are used to maintain

windbox to furnace DP and Fuel air support forcoal and oil elevations. These actuators areoperated through 22 nos. E/P converters, eachsupporting 4 Power Cylinders in each elevation.



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DOUBLE ACTING POWER CYLINDER

IS USED FOR SADC ACTUATORS


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