Mill Reject 4r2f24

Indian Power Stations 2011

Farakka

13 – 15 February , New Delhi

PERFORMANCE IMPROVEMENT BY AUTOMATIC OPERATION OF STAGE-1 MILL REJECT SYSTEM AT NTPC, FARAKKA

Snehasis Bhattacharyya , Sr. Supdt. (C&I) , NTPC Ltd, Farakka

Arendra Kumar Arya, Sr.Engineer (C&I) , NTPC Ltd, Farakka

Farakka

PRESENTATION ROAP

•INTRODUCTION

•DESCRIPTION OF MILL REJECT SYSTEM •NATURE OF PROBLEM

•INNOVATIVE APPROACH •IMPROVEMENT ACHIEVED •CONCLUSION

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Introduction

• •

NTPC,Farakka has 3X200MW units and 2 X 500 MW units Each 200 MW unit consists of:I. 6 no. Bowl Mill II. Model XRP-803 III. Capacity 45.8 Ton/hr IV. Speed – 53 rpm V. Crushed coal at inlet – 25 mm

Farakka

Introduction

•

The 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 through 200 mesh ( 0.075 mm) and 99 % will through 50 mesh (0.300 mm)

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Introduction

The 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 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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Introduction •

Each 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 GATE

I/L Power Cylinder

OUTLET REJECT GATE

Reject Chamber

O/L GATE

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POWER Cylinder

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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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SCHEME FOR MANUAL OPERATION

IA AIR SUPPLY

Inlet power cylinder

Manual Switch

Outlet power cylinder

Manual Switch

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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 Problem This 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 Approach •

Operation 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 required in the mill area

of

operator

not

Farakka FACE PLATE FOR MILL REJECT GATE OPERATION

Farakka LOGIC DETAILS

Modified Scheme

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AUX RELAY - 1 INLET GATE CMD FROM LOGIC

DO CARD CH - 1

24 V O/P

24 V RELAY

Ph N

AIR SUPPLY

Inlet power cylinder

SOLENOID VALVE

AUX RELAY - 2 OUTLET GATE CMD FROM LOGIC

DO CARD CH - 1

24 V O/P

24 V RELAY

Outlet power cylinder

Ph N

AIR SUPPLY SOLENOID VALVE

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Innovative Approach •

In 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” mode

GAIN

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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/hr

B)

Average bleed air temperature at full load (T1) = 2800c = 553 K

C) Average ambient temperature (T2) = 300c = 303 K D) Specific heat of hot air at constant pressure (Sair) = 1.006 KJ/Kg/K E)

Average calorific value of coal = 3200 KCal/Kg

F)

Cost of coal = Rs. 4.0/kg

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/HR

q

QLOSS = 2515000 KJ/HR = 600697 KCAL/HR

q

QLOSS = 600697/3200 = 188 KG/HR Of Coal Equivalent

q

QLOSS = Rs. 752/- PER HR

q

Annual 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 OF MANPOWER ASSUMPTIONS: A) At least 4 nos. of skilled manpower required for round the clock reject gate operation

B) Cost of 1 skilled manpower = Rs. 325.00 CALCULATION: 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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CONCLUSIONS • Continual 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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ACKNOWLEDGEMENT Sri 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 YOU

Farakka