Mill Reject

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

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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)

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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

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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

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IntroductionEach mill has one Inlet & one Outlet Reject Gate

Periodic operation & proper functioning of reject gates is very much essential.

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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.

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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

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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 .

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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

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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.

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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

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CONCLUSIONSContinual process.

Intangible Gains : Employee satisfaction, Better plant personnel safety, Reduction in frequency of mill chocking Minimizing chance of dust ingress in UCR

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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.

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THANK YOUFarakka

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