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Coal Mill Reject
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Snehasis Bhattacharyya , Sr. Supdt. (C&I) , NTPC Ltd, Farakka
Arendra Kumar Arya, Sr.Engineer (C&I) , NTPC Ltd, FarakkaPERFORMANCE IMPROVEMENT BY AUTOMATIC OPERATION OF STAGE-1 MILL REJECT SYSTEM ATNTPC, FARAKKA Indian Power Stations 2011 13 15 February , New DelhiFarakka
FarakkaPRESENTATION ROADMAPINTRODUCTIONDESCRIPTION OF MILL REJECT SYSTEMNATURE OF PROBLEMINNOVATIVE APPROACHIMPROVEMENT ACHIEVEDCONCLUSION
IntroductionNTPC,Farakka has 3X200MW units and 2 X 500 MW units
Each 200 MW unit consists of:-6 no. Bowl Mill Model XRP-803Capacity 45.8 Ton/hrSpeed 53 rpmCrushed coal at inlet 25 mm
Farakka
IntroductionThe source of coal used at Farakka is coming from 23 different open cast mines
In pulverized coal the coal is ground so that about 70 % will pass through 200 mesh ( 0.075 mm) and 99 % will pass through 50 mesh (0.300 mm)
Farakka
IntroductionThe coal supply carries a certain percentage of over burden of stone pieces get leached and come directly into the mills through the bunker though manual stone picking system deployed at coal handling plant
Farakka
Introduction
When these come under the roller, the roller lifts up allowing these to pass under.
Then scrapped by scrapper through tramp iron spout to pyrite hopper
Removed periodically. Any material having a bulk density 1.2 tonnes/m3 should be rejected (for coal it is 0.8 tonnes/m3). However sometimes the material to be ground is also rejected
Farakka
IntroductionEach mill has one Inlet & one Outlet Reject Gate
Periodic operation & proper functioning of reject gates is very much essential.
Farakka
INLET REJECT GATEFarakkaI/L Power Cylinder
OUTLET REJECT GATEFarakkaO/L GATEPOWER CylinderReject Chamber
Nature of Problem
In stage-1 ,each gate is opened/closed by the pneumatically operated power cylinder
Accumulation Cycle : Inlet gate is opened & outlet gate is closed for some time.
Rejection Cycle : Inlet gate is closed & outlet gate is opened for some time.
Farakka
FarakkaSCHEME FOR MANUAL OPERATION
IA AIR SUPPLY
Manual Switch
Manual Switch
Inlet power cylinder
Outlet power cylinder
Nature of Problem
In stage-1, Inlet and Outlet gates were operated with the help of a manual switch
Operation by experience & communication from control room.
Continuous deputation of operator
Frequent operation of reject gates required during high rejection Farakka
Nature of ProblemThis results:-
Hot air containing coal dust coming out of the rejection chamber
Increase the chance of failure of control instruments and has potential to catch fire in control cable.
Transportation of rejects from the mill become troublesome & unsafe for the operation personnel Farakka
Innovative ApproachOperation from newly installed DDCMIS was felt
Remote as well as automatic operation of reject gates can be done efficiently from Unit Control Room
Continuous deputation of operator not required in the mill area
Farakka
FarakkaFACE PLATE FOR MILL REJECT GATE OPERATION
LOGIC DETAILS Farakka
FarakkaInlet power cylinderOutlet power cylinderModified Scheme
DOCARDCH - 1
INLET GATE CMDFROM LOGIC
24 VRELAY
Ph
N
24 VO/P
AUX RELAY - 1
AIR SUPPLY
DOCARDCH - 1
24 VRELAY
Ph
N
24 VO/P
AUX RELAY - 2
AIR SUPPLY
OUTLET GATE CMD FROM LOGIC
SOLENOID VALVE
SOLENOID VALVE
Innovative ApproachIn Manual mode both gates can be opened independently
Auto mode is having priority
In Auto mode Inlet gate will remain open for T1 time and outlet gate will remain close. After T1 time is elapsed inlet gate will close and outlet gate will open for T2 time .
Farakka
Improvement Operational Flexibility
Deputation of Manpower for local operation is nil.
Opening & Closing time (T1 & T2) of Inlet & Outlet gate can be tuned based on requirement
Avoidance of Mill operation in Blasting modeFarakka
GAIN
TANGIBLE GAIN :-I) ENERGY LOSS CALCULATION: -When mills are operating with open pyrite gate condition allowing bleeding of hot primary air through pyrite system.ASSUMPTIONS:A)Quantity of hot primary air, bleeding through pyrite box at a pressure of about 700 mmwc (Mair) 10 T/hrB)Average bleed air temperature at full load (T1) = 2800c = 553 KC)Average ambient temperature (T2) = 300c = 303 KD)Specific heat of hot air at constant pressure (Sair) = 1.006 KJ/Kg/KE)Average calorific value of coal = 3200 KCal/KgF)Cost of coal = Rs. 4.0/kg
Farakka
GAIN
TANGIBLE GAIN (contd..)
CALCULATION:q Energy Loss Per Mill (QLOSS) = MAIR x SAIR x (T1 T2)q QLOSS = 10 x 1000 x 1.006 x (553-303) KJ/HRq QLOSS = 2515000 KJ/HR = 600697 KCAL/HR q QLOSS = 600697/3200 = 188 KG/HR Of Coal Equivalentq QLOSS = Rs. 752/- PER HR qAnnual QLOSS = 752 X 365 = Rs. 2,74,480/- Per One Blasting Hour/Mill/Day
At Farakka , normally 5 mills are in service.
Farakka
GAIN
TANGIBLE GAIN (contd..)
II) COST SAVING ON ACCOUNT OF MANPOWER ASSUMPTIONS: A) At least 4 nos. of skilled manpower required for round the clock reject gate operationB) Cost of 1 skilled manpower = Rs. 325.00CALCULATION: Annual Manpower cost = Rs. 325 X 4 X 365= Rs. 4,74,500.00
Total Annual Saving (I +II) = Rs. 7,48,980.00
Farakka
CONCLUSIONSContinual process.
Intangible Gains : Employee satisfaction, Better plant personnel safety, Reduction in frequency of mill chocking Minimizing chance of dust ingress in UCR
Farakka
ACKNOWLEDGEMENTSri P Tiwari, AGM (O&M) ,
Sri A K Mukherjee , AGM (Maintenance) ,
Sri A Ghosh, AGM (C&I) ,
Sri C K Sarkar , DGM(C&I)
EEMG & Operation Department.
Farakka
THANK YOUFarakka
Farakka
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